Have you tried 'iwconfig' to see if the AWUS shows up? I just did the same install and mine worked right away.
The r8187 driver should work and comes already patched for packet injection with Backtrack 4. The rtl8187 driver should also work, but when both are installed, one or both will break.
FYI, there are two main drivers for this adapter, the mac80211 (rtl8187) version and the ieee80211 (r8187) version.
Here's some more info; has explanation of differences between two types of drivers, how to blacklist unused driver etc
But ideally, it should be showing up in iwconfig straight away when you plug it in.