DL/INSTALL PROBs.

i built my computer and put windows xp on it everything was going fine untill i try to install certain things or download and install and i get unusable errors or file is corrupted or filemissing blah blah etc...on porgrams like Benchmark 05 or even itunes the latest version or trying to download patches for my games i it is really annoying i d/l demos of games it runs into some kind of trouble some things will work, my friend put some files on a disc and they work such as winamp Benchmark 06, i also seen a thread that it could be faulty RAM so i swapped it and it worked for one program Morpheus but now same trouble and i run the most up to date norton anti-virus somebody help plz..

 

MB ASUS A8N-SLI Deluxe NF4SLI 939
CPU AMD|A64 3700+ 2.2G 939 1M R
MEM 512x2|CORSAR TWINX1024-3200C2PT

 

MB ASUS A8N-SLI Deluxe NF4SLI 939
MEM 512x2|CORSAR TWINX1024-3200C2PT
CPU AMD|A64 3700+ 2.2G 939 1M R
Western Digital 80 Gig HD
i swapped my gig of ram for my old 512 and i manage to get a program to work so im sending my RAM back to get replacements but i hope their compatable im pretty sure they are...