I have a Dell inspiron 5150 3.2Ghz laptop that I use. I run Vegas 5 with no problems at all. It has a 4pin firewire connector. I've captured hours from my cam to a USB2 Harddrive.
I got the laptop about a year ago for $1500. I would probably go with a P4 HT processor if I was going to buy another.
I use a Toshiba satellite p25 s607. It has a 17" screen, built in four pin firewire, DVD burner and a swappable second hard drive bay. It's huge but it works really well. I use it with Premiere Pro, Cubase, and a Firewire 410 audio interface. My starving musician friend constantly borrows it to use as a mobile recording studio.
DMN Forums just gave a great review on the Alienware Laptops. They're pricey but I hear they rock.
I've got a P4 3.06HT custom built jobbie from a local vendor here in Salt Lake. I'm trying to get them to build more A/V machines because their systems rock. 'Puter cost me around $1900.
It really depends on your needs. LCD size? 4pin or 6pin firewire? Wireless networking? Speed of hard drive?
I wanted someone local who could fix the system in a jiffy if needed. I did have a temporary HP laptop I bought from Costco with the same specs as this one but only 512mb RAM -
It was heavy and I didn't like the case but it never gave me any problems. Costco also has a 6 month return policy on computers. I don't think there's anyone out there that comes close to that.
Definatly check out Sager laptops! They are soo freaking Cheap and you get soo much for the money...I would recogmend that you get a laptop witrh hyper-threading, dual channel memory, a deseent Graphics Card (128MB Ram or More) and a 7200RPM HD for shure...Check out Pctorque.com, they are an excellent reseller. Thats where I got my Sager 5680. They got the best prices on Sagers. http://notebookforums.com/ if you want an excellent forum too!