The only advise I can give, is don't buy a celeron processor, go for a pentium4 or preferable qa centerio thingy or a amd 64 type. Hard-drive and memory size will be all important. the biggest hard drive you can get(video takes a lot of space for transfering) with the memory the larger amount the better, when I was looking at my laptop, I found that most did actualy share the graphic card memory with the main memory, so if the graphics mem is 128mb, if you've got 512mb on you laptop, then you realy end up with 383mb ish to run your os and any applications you running. So I would suggest that you look for a min of 1012mb, and ask if you can up-grade higher.
Also I hope that you don't intend to try to edit while using the battery, it quite a labour intensive activity, on power supply, memory and cpu (hence celeron is hopeless)so I would suggest that when you editing keep to the mains adtapter.
and I would strongly suggest that you double check that that you have both a firewire connection and that the dvd does actualy write, there is a lot of cheap and expensive lappies out there that read dvd's but only write cd's (you be amased)
When choosening remeber, with lappies it is very difficult to up-grade, and has I found when I brought mine, there seems to be little information on what is up-grade able and what is not.
I hope this helps a little