During the installation of
Street Atlas you should be able to change the default location. It will usually default to c:\program files\... but you should be able to change that and it will install the whole thing into the alternate location. 8GB thumb drives are getting pretty cheap these days and that should solve the problem.
Sorry I can't be more specific because it's been a few months since I installed Street Atlas. It should be easy enough to start up the installation and walk through the first couple of steps to get to the installation location and see what options you have, then cancel the installation and decide how you want to proceed (eg. thumb drive, USB hard drive, whatever).
...ken...