You could consider using the .net client profile. It's a slimmed down version of the .net framework that comes with most of the general stuff of client apps, but none of the server stuff (like asp.net). I haven't timed it, but I presume it would install quicker.
Unfortunately 3.5 client profile is pretty rubbish and comes with a load of caveats. (Like you have to use the web installer, and it will default back to the full fat version if it detects any
other .net on the PC already, and is for 32bit OSes only).
If you can hang on until 4.0, the 4.0 client profile looks to be much better. It will have a re-distributable download, and won't fall back to the full thing. Check out the table titled "Enhancement in 4.0 Client Profile vs. 3.5 SP1 Client profile:" in this blog post
(For more info on the 3.5 client profile deployment - see here