You can't fail if you get the Presonus stuff. I have the 8 input FirePod, but the 4 input Fire(thing) is fine for most applications. If you drop 300-400 bucks you can get something that will sound professional. If you want to spend less, an Edirol product will do you right.

Many of these units have decent preamps in them. Obviously a dedicated fancy one is best, but if we're talking about replacing a 4-track cassette unit, you will be amazed at what you can make with a laptop, interface and decent mic.

Don't scrimp on the interfac if you can help it. If you have a choice of computers, I can't say anough good things about Macs.

I would second the Presonis firepod. It also has two matching inpedance inputs for DI ing. (you might want a dedicated di if you want to amp at the same time). The Presonis cuts through the mixer issues due to the pre amps which you get 8 of on all inputs which are well reviewed at the price you can chain them togeather (this includes the firebox) if you should need more inputs. It sets up easlily and has phantom power on off on all inputs in groups of 4. As well because it is a outboard unit it does not pick up electrical noise from you computer. May not be the answer for you but a nice all in one solution.

One thing to look at on cards and computer is the bottom end response. Many will give you good high end but not go down into the bass range that you are picking up on your mikes.

In addition to the sound on sound reviews check though google what people who buy them on boards say I found that reveiling when shopping for gear. Some gear is not well backed up with support.

As well when you get more than 4 inputs you should be sure that your hard drive spins at a fast enough speed to record - you might need to get a faster internal hard drive to deal with audio stream rates.

I do this quite a bit; the Onyx firewire interface works great with my laptop. 16 channels, monitoring (with some latency), 24 bit/48k (it can run at a higher rate; this is what I do...), and it works like a champ. The preamps on this interface are actually decent, although they are still crap compared to, oh, say a Neve. For homebrew digital recording with a firewire laptop, try out the Onyx.

Did that sound like a sales pitch? Sorry...it is the only interface I have really worked with.

Not an expert on the subject, but I bought one of these recently and I totally love it:

http://www.zzounds.com/item--ALEMULTIMIX8FW

Considering what you're getting for the price, it really can't be beat.