Constant corrupt downloads for patching games and antivirus

First off, I have just acquired a new dsl connection a week ago when downloading patches became a problem. What happens is that the download appears successful, however when I try to install some problem always occurs that means the file is corrupt.

For Vampire:Bloodlines, I install patch and game is nonfunctionable as it cannot load engine.dll file. For Warcraft 3:TFT, it cannot authenticate archive when attempting to install patch. For BF2, it errors due to a incomplete memory read. For Norton virus definition, it never successfully installs itself. These files have been downloaded several times and through different websites to test the problem.

I have 3 possible conclusions for the problem:

1)Conflict with firewall. (I have checked for all firewalls on my computer and disabled them, such as Nvidia firewall and Windows firewall.)

2)Virus corrupting all downloads. (I attempted virus scan with 2002 virus definitions and have found nothing.)

3)Conflict with some feature of my dsl. (My dsl provider is Consolidated Communications and dsl required no installation of software.)

I would really appreciate any help because I cannot play multiplayer on any current games without the required patches. Thanks in advance.