corrupt files

Ok everytime i download a file or installer e.g. windows xp service pack 2 (this is my related to my previous thread) windows comes up with the error that the file has been corrupted or damaged.
When i download the exact same file on a differnt pc and copy it to my HDD via network connection, there is no problem. I have intstalled all programs i wanted this way but its just very annoying to download progs on different pc all the time, that's not why i created a network

 

Try reinstalling tcpip?

 

Hm, i dunno...
I had a windows reinstall like 4 times before i figured this out