if your tank is drilled and you need a pump here is what I use on my 55 Gallon tank:
http://www.marinedepot.com/md_viewItem.asp?idproduct=DN1127
if you get some hose from home depot and an 18 gallon rubermaid tub you could have a sump and pump for less than $100.00
18 gallon rubermade tub @ target costs about $6.00
water tubing -- "spa Hose" from home depot is about $10-20
depending on what size you buy.
mag 9.5 69.95 plus shipping.
you can replace the rubermaid tub with a nice sump tank later...
or if you can find the right place to put it just modify the lid to have holes for the water lines....
EDIT: sorry I just read a bit more, you may need some other parts:
bulk head fittings like this:
http://www.marinedepot.com/md_viewItem.asp?idproduct=FT1113
possibly some return fittings like:
http://www.marinedepot.com/md_viewItem.asp?idproduct=FT0001
and possibly a "stand pipe" like this:
http://www.dursostandpipes.com/
note that most of this is just PVC pipe you can buy at any hardware store and make up to suit .... hack saw and a drill can help ....
look at photos here of folks setups.
the "return line" is generaly a pipe from the pump that ends with some kind of adjustable nozzle to put water back into the tank.
the "overflow" is just a large pipe that allows water to fall to the sump. works my gravity to move the water.
if you have a tank made by "All Glass" you can buy a kit with the parts for your tank.
http://www.all-glass.com/products/aquariums/index.html
if it's some other tank you may or may not be able to use that kit.
hope this helps you start to figure out the plumbing.