I bought fallout new vegas on the disc, so i installed the 6gb then steam applied the patch like usual, once the patch was complete i launched the game, however only the option to install was available, i click install (despite having done so already) and receieve this message:
"Fallout: New Vegas does not appear to be installed and the installer could not be found. Try exploring to your DVD-ROM drive and selecting setup.exe to install the game."
However my disc is still inside the DVD drive. I have also tried to delete and reinstall however the same problem applies, and have then also taken out the disc deleting the game and have spent 3 hours downloading from steam only to recieve the same message.

bump

try this, uninstall steam and install freash from the CD/DVD. It should install steam, then immediately install the game off of the disc.

TY so much it woked

I've tried this twice and each time I still get the "game does not appear to be installed" message. Also tried validating game cache via steam > fallout new vegas > properties > local files. This finds 1 missing "files" which steam downloads, but the game still "does not appear to be installed" afterward.

Any helpful advice to resolve this situation would be really wonderful.

Success!

I tried reinstalling steam & FNV to the default location instead of the larger drive I'd been installing on previously.
Also set falloutNV.exe and falloutNVLauncher.exe to run as admin based on advice found on these forums.

One of these changes did the trick because I'm playing the tutorial now!

I'm really liking Games for Windows Live a lot better right now for purchased disks for activation and installation. This Steam crap is for the birds.