Several programs unusable

I tried the Read and Run Me First. I made it to step 4 and am unable to download any of the programs.

Unable to download some programs is one of the problems I am having. I am using Avast and it is actively working but I am unable to start up a system scan. I am able to download avast but it will not install. I also am having problems with other virus scan/spyware remover programs to install. Hi jack this will not run Adobe photoshop will not run either. It is a strange problem and seems to affect a variety of .exe files. I have also tried online virus scanners with no luck.

I am running Windows XP SP2.

Any direction or help would be appreciated.