Go grab a copy of virtualBox, hunt around for a dead laptop or outdated XP machine that still has the XP sticker on it for a key – install XP in virtualBox under your favorite pet OS, and done.
you can even make multiple installs to test multiple versions native.
I test 9 native on Win7, It’s IE8 testing mode seems trustworthy enough – but have separate XP installs in VB for 6 & 7… and a 98 install with 5.5 and IE6 as there are some behavioral differences between 98 IE6 and XP IE6.