EDIT--^^^I guess I spent too much time searching and typing.

Here's a thread I found with pics showing 6x9's installed in the dash.
*Credit goes to vwaltdog for this thread.*

As you can see, you have to cut into the heater ducts. but you can make them fit.

If you do some searching in the archives, you'll find lots of threads about installing 6x9's where the 4x10's are supposed to go. However, a lot of us will tell you that you'll get much cleaner sound out of a pair of round speakers with tweeters; opposed to a set of oval speakers.
*Kinda like DjDraggin did with his Fiero.*

Here's a thread discussing round versus oval speakers.
[This message has been edited by Deabionni (edited 01-10-2006).]