Two things to look at.....
Go to Start >> Settings >> Control Panel >> System
A box will appear on the screen...... under the "System:" part, there are four lines, which (on my system) say.....
Microsoft Windows XP
Professional
Version 2002
Service Pack 3
What does yours say ?
Then, in Internet Explorer, click on Help, then About Internet Explorer .........
What version does it report ?
Nick.