Wow, thats really weird...I can also use steam without incident (I can even play Half-Life 2,
... Half-Life 2 doesn't even run for me if I get Steam to start up.. it goes to fullscreen, and freezes the screen (without covering anything up). I am suspicious of hidden dialog boxes (like in GTA), but I haven't tried to investigate that problem in detail yet.
the only issues I get are some intermittent sound lags.) Perhaps there's something wrong with your RAM? Have you tested any other apps that use about as much as Steam uses (about 200 MB max in my experience) on either WINE or native apps?
Xorg? Warcraft 3? Gnome? KDE ? Doom 3? I've had Half-Life 2 working back with Oliver's very first patch.. or with Cedega..
I think hardware problems with the RAM are highly unlikely. I've had plenty of those, and when your RAM is defective, nothing works - you get spurious kernel panics, and you will find out that it's defective really soon.