Mark,
Excuse me if this is too basic.
To check which version you are using click on the HELP menu on the top of your browser window.Select the "About Internet Explorer" option.
It should say Version 6.0.xxx.xxx
If it says Version 5.0 or 5.5 or similar you are definitely running an old version which many web-sites(including IAS) are not written to recognise.
If this is the case I suggest you go to Microsoft's web-site and download version 6.
Once again apologies if this reply is telling grandma to suck eggs.