Mark
I've tested out Windows 2000 with both IE 5 and IE5.5 sp2 (the only 5.5 version I could get hold of) and both worked ok so I'm not able to replicate the problem you are having.
Can I suggest that you try another browser such as Opera or Mozilla or upgrade to IE 6.
Thanks for having a go.
Keep checking back to PurpleAds as there will soon be many thousands of ads to browse through. 
Cheers, John
Madabout-kitcars