Why are my Zip files corrupt?

[Hubris]

I tried to download a couple zip files last night, as well as this morning, and they've all been incomplete. When I right-click on the file it reads the correct size, but when I open it with either WinACE, WinRAR or WinZIP (I've tried all three), there is only a fraction of the files inside. What the hell is going on? I'm running WinXP and the latest versions of all those programs. Help?

 

[Horsepower]

I had a similar problem once, and it ended up being a memory stick gone bad.

 

[Hubris]

Ah crap. If that's the case, why the hell couldn't it have happened six months ago when memory was cheaper than dirt. Hope that's not it.