Check out Fabrique Nationale's Five-seveN handgun. I am pretty sure it uses the same ammo as the PS90 carbine. It might be a good setup if money is not a concern. The Five-seveN handgun retails for $1000 and the PS90 retails for around $1800.
http://www.fnhusa.com/products/firearms/family.asp?fid=FNF003&gid=FNG001
http://www.fnhusa.com/products/firearms/family.asp?fid=FNF009&gid=FNG006
Another alternative would be to pick up a Glock 19 and a Hi-Ponit carbine. I have read that you can pick up the carbine for as cheap as $200 and the Glock will cost you around $500. I am fairly certain the hi-point carbine accepts the glock magazines.
http://www.hi-pointfirearms.com/40_carbine.asp
The last option that I can think of besides a custom setup would be to go with the berreta Px4 and Cx4 Storm setup. I actually thought about picking something like this up since I was in the market for a good 9mm. The carbine is pretty pricey and I haven't read about a lot of people who have used it but those who have had good things to say. The only problem with gun reviews is that no one really has anything bad to say regardless of the product.
If you can find a good carbine setup to go with a Glock you would be in good shape. I like the Five-SeveN but it is expensive!
"Chance favors the prepared mind" - Louis Pasteur