That also applies to photoshop cs owners as well.
The reason the specs say windows 2000/xp is because those were the current operating systems cs2 supported when released in 2005, well before windows 7.
Photoshop cs2 should work on windows 7, but as always there is no guarantee photoshop cs2 will work without some glitches on windows 7.
If your hesitate about trying it, you can always buy photoshop cs6 or subscribe to photoshop cc 2014, both of which are specified to work well on windows 7.