Okay. You can hook up the sub, but it won't work the way that a traditional 5.1 set-up would. That receiver has no bass management (i.e. doesn't direct bass from speakers to a sub) and is not set-up to utilize a subwoofer. Also, because it doesn't include any decoding or inputs for discrete 5.1 audio tracks (such as Dolby Digital), there isn't any discrete .1 subwoofer audio to go to a sub.
However, if you want to add a little rumble to your system, you can give this a try. You could connect the subwoofer to one of the RCA audio outputs on the back of the receiver (either from the "TAPE/MD" audio outs or the "VIDEO" audio outs). If you have an RCA y-adapter, that would be great, because you could connect both left/right RCA outputs on the receiver into the single RCA input on the sub. If you don't have one, you can always just connect one of the outputs (either left or right) to the sub for now.
I recommend starting with the volume of the subwoofer turned all the way down, then turn it up gradually until you reach a level that you like. Also, try the "MUSIC/MOVIE" switch to see if you prefer either setting.
Because the reciever doesn't do any bass management, and because the subwoofer doesn't have a crossover dial (that I can see), you can't control which frequencies get played through the sub. So, you might even hear dialogue through the sub, which might be annoying. However, you can always hook it up and check it out.
EDIT: I see that Jerry covered some of this while I was typing.