Extremely slow when guest WinXP is launched

[isend]

I run virtualbox with guest Windows XP Pro on Mac OS 10.6.8 on both MBP 13" early 2011 and iMac 21.5" late 2010 (both with RAM 2G*2). Both machines are fast when virtualbox is not running. When WinXP is launched, iMac is still fine, but MBP becomes extremely slow. I use the same settings on both machines:


On MBP, this is what iStat Pro shows before I launch guest WinXP:

and after WinXP is launched:

Usage of RAM is seriously boosted. How can I make my MBP run as smoothly as my iMac (without upgrading RAM)?

[Perryg]

Lower the amount assigned to the guest, shut down host programs/services, or add more RAM.
XP will work at 512MB. I compile with VS2005 with 512MB.