Congratulations Tom!!!
Lots of folks already put some good advice in. I have our car seat mounted in the back of my Turbo-brick and use the "clip" to lock the lap portion of the belt through the seat. The inertia reel is in the shoulder length, and can still move, but the lap belt portion is locked firmly and holds the seat strongly and securely.
We had the "car seat guy" look over the installation and he made a few good suggestions too. Definitely find the local expert. They know their stuff.
A friend of mine might sell me a used Recaro booster seat. Wouldn't that be perfect? :-)
Right now, Sara is still not quite big enough to fit in a regular seat, but she's already got the driving posture down pat!!
(this pic was about 3-1/2 months ago, so ya never know!
Again, congrats Tom!!
Oh, and get crackin' on the car. You have even more to do than I did!! And it's really true, you will so little time once the baby is there, you'll think an uninterupted 30 minutes is spectacular! That is, of course, if you're not already sleeping...
-Josh2