Couple of questions:


IF (big if) I get the retail DVD:

Can I install the game on any directory/drive I want?
Once the game is installed and activated and I set Steam to offline (and I am assuming that means Steam client doesn't connect anywhere, right?), since the client needs to be active, is it still going to mess up with the game, as in erase savegames, ini files, and such?

Only way that can be done is if you install steam in the directory you want. Steam gives you your achievements , tracks your leaderboards.

Your other option, if you use NTFS, is to use an NTFS Junction to create a symbolic link from the steamapps/common directory to the place you actually want it.

Info:
http://en.wikipedia.org/wiki/NTFS_junction_point
http://support.microsoft.com/?kbid=205524

Required tool:
http://support.microsoft.com/?kbid=205524

If you have Vista/Win7 then use mklink and use Junction points for XP/2000 but make sure to read how to use linkd to remove junction points if you're going to work with them (don't have to worry about symlinks, they remove the normal way).

You can cut/paste your steam folder from drive to drive (I've moved mine a few times) without any adverse side effects (atleast in my case).

Here is a Vista/Win7 example of how to symlink Fallout NV's steam folder to c:\games so it exists in the steam folder but shows up in c:\games. Don't try to use these unless you know what you're doing or you'll probably get confused and have to redownload the game from steam cause steam can't find it's folder anymore:

For Windows Vista/7 64-bit:

mklink /d c:\games\falloutnv "%ProgramFiles(x86)%\steam\steamapps\common\fallout new vegas"

For Windows Vista/7 32-bit:

mklink /d c:\games\falloutnv "%ProgramFiles%\steam\steamapps\common\fallout new vegas"

Here is an example of the opposite, if you have cut/pasted it from the steam folder to c:\games\ and then want to place a symlink in the steam folder which points to the real c:\games location

For Windows Vista/7 64-bit:

mklink /d "%ProgramFiles(x86)%\steam\steamapps\common\fallout new vegas" "c:\games\fallout new vegas"

For Windows Vista/7 32-bit:

mklink /d "%ProgramFiles%\steam\steamapps\common\fallout new vegas" "c:\games\fallout new vegas"