You realize that OSX has no TRIM support as well, and the issues facing XP are the same with OSX (SSD related). Many SSDs (like the toshiba and sandforce controllers) have their own basic garbage collection routines and many over provision to keep performance top notch. My point is, don't worry about this and focus on other factors.
My main point is that XP is an old operating system and Windows 7 is a new one that is optimized for modern hardware. Windows 7 gets a big performance boost from the SSD, similar to OS X, while XP does not. I noticed as much on my old MacBook Air when I upgraded my Boot Camp partition last year from XP to Windows 7.