I already had an updated Steam client before attempting to install FNV.
So I connect to the internet and launch Steam. After I enter my password, the Steam login screen stays up and I download about 2mb before Steam loads. This takes around 10 minutes. This is normal and what I experience every time I log into Steam. I throw the install disc into my drive and wait... no prompt so I click on add new game. I put in my serial key and Steam verifies it. No prompt, so I click on install, next and oops. I'm downloading it now instead of installing from the disc. My fault, I hit cancel. Steam locks up. I have to bring up task manager and end process.
I log into Steam again. Same 10 minute process. I get it back up and install the game from the disc. While the game is installing, I notice the addition of FNV to my games library. I try to head off any sort of launch day updating so I click on it and hit properties and change the update setting to "don't update automatically". I hit ok. Steam locks up again. Task manager, end process.
I log into Steam again. 10 minutes later I'm installing the game again. I get through the install and am informed that an update will now start automatically. In fact it has already started before I hit ok on this box. I check the "Downloads" page and it looks like I need 16mb to be up to date. Ok, that's not terrible. It takes about an hour and a half for me to dl that much.
Two and a half hours later, Steam has downloaded 32mb, applied 16 and I now have the option to play. I click Go offline and disconnect from the internet. I hit play. I then watch a box that says "Preparing to launch FNV..." for the next five minutes while the dots at the end ascend from one to three and over again. Finally I hit cancel and beside Fallout New Vegas in my library the message "update paused" appears.
I log into Steam again. 10 minutes. I resume update and go to download page. It now needs a total of 8.2mb. Ok, not terrible, that should take less than an hour. An hour and a half later after Steam has downloaded 16mb and applied 8.2 I have the option to play again. I click play while connected this time and it loads. Great. So I exit. Click "Go Offline" and disconnect from the internet. I have been playing no problem, offline, since.
I have had some experience with this in the past, so I wasn't expecting to be able to play it as soon as I got home. Imagine, and it is easy to imagine considering that this is a single player game, that this is someone's first experience with Steam and dialup. I even started with an updated client. In total it took a little more than 5 hours to get it running.
