I'm a happy user of Virtualbox on Linux. I mostly use Virtualbox to run WinXP guests on my Linux host so I can use Korean Internet banking services and shop online in Korea. You might ask, "Why do you need an ancient Windows OS just to do Internet banking?"
Some background on this situation: in the late 1990's, prescient Korean bureaucrats decided to implement PKI (Public Key Infrastructure) for all online transactions. Since existing open standards for PKI were still in the early stages back then, the Korean gov't rolled their own solution which was implemented through ActiveX plugins for Microsoft's Internet Explorer web browser.
Fast forward 15 years -- the web has evolved but the Korean PKI standard is still unchanged and all Koreans are forced to keep using old ActiveX plugins which have been left in the dustbin of history. Shopping and banking online in Korea is a hugely frustrating experience, as you must download and install new ActiveX plugins almost every time you start a new session. Although nominal Internet speeds are quite fast (several times the speed of American Internet) in practice most Korean users cannot benefit due to all the cruft they are forced to install to use native Korean Internet services (which are still optimized for the IE8 web browser).
Although IE has > 80% market share in Korea, online banking and shopping sites only support IE's older incarnations. Good luck getting modern versions of IE (11+) working on, say, the websites of Woori Bank or Auction Korea.
On modern Windows OS's, however, more recent versions of IE are installed by default. If you're one of the millions of Koreans still using WinXP, that's not a problem because IE8 is the most recent version of IE compatible with that venerable OS. For those not using XP, however, using the Korean Internet is often problematic. For example, my girlfriend's computer runs Windows 7 with a modern version of IE but she sometimes can't use certain Korean sites requiring ActiveX.
The solution? Use virtualization -- Virtualbox, VMWare, Parallels, etc. As I mentioned earlier, I use Oracle's Virtualbox. In the past I installed WinXP onto a fresh VM using an old .iso from MSDN. Even the most slimmed-down install with extraneous features omitted came in at just under 10 GB with no custom applications installed.
Whether using dynamically-allocated partitions or not in Virtualbox, after installing a few key applications for Korean banking, shopping and word processing (in the form of Hancom's infamous 한글 200x series) partitions soon balloon to 15GB or more.
Enter WinXP VM's provided directly by Microsoft through their ModernIE site -- for Virtualbox on Linux, we import a compressed OVA file that blows up to a regular VMDK image file. The bare-bones WinXP VM only takes up 1.9 GB on initial boot! Compare that to ~ 10 GB for a clean install from .iso or CD.
For users in East Asia, however, the VM cannot be used as-is because the default VM image is of a US version of Windows. Prepping the VM requires the following steps (which requires a WinXP install CD or .iso from MSDN):
1) Extract the necessary install files from the WinXP install CD or .iso - extract the entire /i386 directory from the .iso to some directory, then use the Virtualbox "shared folder" feature to make this directory readable by the WinXP guest.
2) Enable East Asian Font Support -- go into Control Panel and select "Regional Settings & Languages" and make sure the box for "East Asian Language support" is checked. The installer will then ask for the WinXP CD or a location where the installation files reside. If we point the installer to the shared folder /i386/... the language file installation will go forward. The path changes a few times during the install, so you may need to enter the /lang subfolder and then later point to the parent folder again.
3) Install East Asian Language IME (Korean, in my case) - go into Control Panel and select "Regional Settings & Languages" once more but this time click on "input methods" instead of "languages"-- now choose Korean and make it the default. After a reboot, pressing the Hangul key (Right Alt on non-Korean keyboards) will toggle Korean language input.
There are also some Virtualbox-specific VM settings that you might want to change. The default memory setting is 512MB, but I changed this to 1024MB. Also I had problems booting the VM before enabling the Virtualbox "System" option, I/O APIC. For those users who store their Korean banking PKI certs on a USB thumb drive, you will need to enable USB 2.0 in the VM settings and also separately download the Oracle VM VirtualBox Extension Pack and load it from the Virtualbox Manager (under File -> Preferences -> Extensions).
Rearming the WinXP VM after 30 days
Note that the WinXP VM's from ModernIE will only run for 30 days. After that, a dialog box will appear at boot asking you whether you want to activate your copy of Windows. If you click 'No', the system will automatically reboot. Microsoft initially said that taking a snapshot image upon first importing the VM and later restoring that image would reset the activation clock, but this is actually not the case!
When 30 days have expired, what I do is restore a clean snapshot (which will still ask for activation) and then boot into Safe Mode (pressing F8 to bring up the Windows boot menu and selecting 'Safe Mode'). After booting open a Command Prompt and type the following:
Even with a successful activation, there will be no output.
Now reboot into a regular session and the activation clock will be reset to give you 30 more days!
Although Microsoft says that the WinXP VM activation counter can be reset up to 3 times (for a total of 90 days), by restoring a snapshot from a clean install and booting into WinXP Safe Mode and resetting the activation from the command prompt/CLI I've been able to use the same VM for more than 90 days!