I don't think upgrading is really worth it. Well, atleast not for general purposes, neither for BF2.
Windows XP, having been out the dominant OS for the last 8 years, has exactly that advantage. All software developed for the past 8 years has been made and optimized for it. And most known vista/windows 7 only software/games have some how or another been cracked to work on XP. However, people forget that XP aswell was disliked when first released due to many incompatibillities. I'm positive in the future, XP will be as forgotten as Windows 98.