To buy a home or not....

It might be time for me.

I'm looking around and homes are selling for WAY under value right now in my area... I currently have a job and the soon-to-be Mrs. will be getting out of school this December.... I found a house I like, she seems to like it too.... its only 5 mins from my office (BIG SCORE - current commute is 45-60 mins)

They house is in a desirable part of the town - close "The Square" ... where all the restaurants/bars/etc are which is nice... Since I am currently living at home and just saving money for the wedding/house I'm in no real rush... but I found a place.

Could use some improvements but my basically-retired dad is the most handy guy I've ever met, and by best friend who doesn't work in the winter is really handy too - I'm sure they would help with this and that for beer and food....

The place has everything I want on my checklist:
Old home character/charm (not a cookie cutter house)
1600 ft^2 (not including the basement)
4 bed 2 bath (could rent 2 rooms out to my cousins who go to the University in the same city) -
new roof/furnace/appliances -
5 STALL GARAGE!!! AWESOME -
full basement (unfinished)
Basically seems perfect for what I want now... its been on the market for 140 days and is currently listed at only 80k, my guess is a 72k (90% of asking) offer would be taken..... so the mortgage would only be $100 more than I'm spending on gas to/from work... taxes are a stupid cheap $1500 (is first time home buyer tax credit still going?)....

If I ever want out too it is close enough to a University to be a rental.

I looked into insurance, monthly mortgage, taxes, bills.... it would be cheaper than renting a 2bedroom place in the same town.

My question to all of you is this:
If you are 23 years old and can afford it - do you buy a house while the getting is good - or not tie-yourself down?

...Also anyone in the mortage business - do you know what the required/average down payment is these days???
My fiance' insists that we NEED 20% or will NOT get loan...
My dad who has been in real-estate for years said the average person these days pays cash or puts down ~$1500 for every 100k financed.

Which is right?

Thanks!