Right on, thanks guys. Actually, it just dawned on me that perhaps getting a 20" ACD for the MACBOOK might be a better solution. What do you guys think?
I'm not sure about that one. Firstly, it seems like plugging in the MacBook to a display whenever you sit at a desk is a minor thing, but when I had only a laptop I done exactly this and I can guarantee you that it does become annoying. Come in, sit down, put laptop on desk, plug in power cable, USB cable, display cable... it seems minor but it does get annoying. Furthermore, using the keyboard on the laptop means the laptop and its display are always awkwardly in front of the big display... so you either have to live with that or buy another keyboard so you can sit your laptop at the side.
Secondly, if you do decide you want the display anyway then I wouldn't recommend the current Apple displays. They are getting old and are currently quite overpriced. A lot of people thought they were a cert to be upgraded at MWSF. That didn't happen, but I still think they'll be updated very soon. If you want an external display I'd go with a Dell, which have the same actual display unit in them as Apple's do anyway and are about half the price. By the way, despite this I have an ACD plugged into my iMac right now... but I bought it ages ago when they were priced more or less the same as the Dell ones.
I think your options are...
1) Keep the MBP and live off that.
2) Buy a MacBook, 20" screen, a keyboard and a mouse. If you do this remember the mini-dvi to dvi converter for the monitor.
3) If you can somehow stretch to it, buy a MacBook and a 20" iMac.
Whatever machine you buy I'd make sure you have 1GB RAM in it.