The trial version of WinRar 3 can be download at
www.rarlab.com, as can the freeware command line unrar program (under the menu
RAR | Extras), a 131KB download.
If your current zip / archive manager program can not handle rar files, there are several freeware alternatives, including;
7-Zip (930KB),
Filzip (1.5MB),
ICEOWS (740KB),
IZArc (2.7MB) and
WinImp (314KB).
7-Zip is open source and looks promising, though the windows version can not extract multiple files at a time.
The smallest program with good context menu integration is ICEOWS; you can select multiple files, right-click-drag and select 'extract files here' when you drop them into the desired destination folder. However, this program rudely takes over file associations without asking when installed; it is easy to change this in the options, but it does not restore the previous associations. Unless your current archive program can re-associate itself from its options (which is not uncommon), you might need to reinstall it if you don't want to switch to ICEOWS.
In any case, there are not that many rar files that it will make a huge difference if the program used can extract multiple archives at a time or if it has context menu support (most programs remember the last folder(s) extracted to, so you would only need to browse there once anyway).