I'm sorry, I don't happen to have an immediate solution to your problem. However, for future reference, I have had many problems in the past Downloading Programs from places like CNET, rather than going directly to the source when possible.
It has happened to me in the past that Download Sites like that do in fact have outdated versions.
Since this is a clean install, I suppose a System restore is out of the question.
Unfortunately, a repair may be in order. (I would wait for other opinions though).
You might also try to use the System File Checker tool to check the integrity of the system files:
1. Click on Start
2. Click on Run
3. Type "cmd" (without the quotation marks)
4. Press Enter
5. Type "sfc /scannow" (without the quotation marks)
Note: There is a space between sfc and /
6. Press Enter
(It may ak you for your XP CD if required)
If you try avast again after this is sorted out, I suggest you use the link below:
http://www.avast.com/i_idt_1016.htmlI also use XP (Pro) and have had no problems installing and running avast...You'll love it if this problem doesn't get you to down in the dumps.
Good luck!