I've been having the same problem since last night. I'm pretty sure it's a steam issue, but since I've gotten no help at the steam forums, I thought I'd try here.

I cannot install Fallout: New Vegas, because steam never finishes updating. I can install steam, but then it advances to "updating steam platform" and will either advance to 26% before resetting and saying steam is temporarily unavailable, or will advance to 100%, reset to 28%, and then repeat into infinity. I can't even get to the actual installation of new vegas, because I can't get past installing steam.

I've tried everything I can think of. Uninstalling and reinstalling, installing to a new directory, turning off my anti-virus, making sure my firewall has all ports open and allows access to steam. I'm at my wits end here. Does anyone have any idea on what might be the problem?

I'm running Windows 7 64-bit.