Is there any video editing software that will edit a video with a greenscreen? So I don't actually have to be there to film and just fill the green screen up with something else.

Hope someone understands what I'm saying!!

Both Premiere and After Effects have that capability, as I'm sure does FCP and Avid.

Premiere, After Effects, Sony Vegas, Avid, Final Cut Pro, Final Cut Express all have the effect. Under some type of Video Effects tab, it will usually be under....Keying, or Key. Now, some programs have a straight greenscreen filter under this, or you can do Color Key, which lets you select the color that you want to make transparant.

Better hope its well lit! DV is especially hard to key because of the color space compression that's native to the format. The best way to avoid bad keys is to make sure the screen is well lit, and that shadows are kept to a minimum, you can always add them later.

Also keep this in mind. Its good to have the green screen well lit, but also its good to have the subject well lit also. What kind of lights are you working with?

The proper way to light a green screen is to light the screen perfectly. Back the subject way away from the green (or as far as you can if its a bed sheet), then make sure none of the light for the green screen is getting on your subject. Then turn OFF the green screen lights (keep the subject in the same spot) and light your subject, using basic 3-point lighting, or a Key light (main source), fill light (secondary source on the front of his face), and a backlight for the back of his head. Make sure none of this light hits the green screen. Then turn the green screen lights back on and you should have it just about perfect. Just do manual exposure on your mini dv camera to make sure that the green is not getting too bright.

EDIT:
It is NOT going to be perfect. However, if you use something like after effects, which you can get a 30 day trail, you can import your footage, and do a color key. its better at getting that color out that most programs like final cut pro, or premiere. Although final cut pro does have a handy little green screen spill filter that helps eliminate green spill on the shoulders of the subject. After Effects has this as well. Hope this helps.