Advice on Setting Up A Laptop-Based Audio System?

Hey, I'm looking to set up a workspace audio system based around my Apple Powerbook G4. I've got about 100 GB of uncompressed audio on an external hard drive. I currently have Monsoon planar speakers and matching subwoofer hooked into the laptop through the 1/8" audio out, which soundsokay, but I think I could do better.

I don't have a PC card slot in the Powerbook, so I'm limited to a USB audio connection. I'm not looking to hook this system up to my "big rig" -- it's just for my workspace. I was looking to bypass getting an amplifier, unless it's fairly small.

I was thinking of going with some powered mini-monitors and maybe some kind of adapter/DAC in between, but I'm space-constrained and not looking to spend more than say, $600 total.

Any suggestions?
Regalmal: I am just now exploring the viability of laptop control and storage for a music library. Can you explain to me in simple terms what equipment is necessary. So far I have a good HP Laptop that I have sent in to have the HD cleared off and anything else not necessary to managing my system. It will be a dedicated PC. I use a Krell HTS 7.1 pre/pro that has an RS 232 Communication Port for computer use and Krell amps all-around to drive Maggies all around. There seems to be a ton of info on line and herein but I cannot clearly see just what exactly is needed in the way of other equipment. Obviously I would need an external storage unit but that is all I really know. You seem to have it working pretty well. Puerto
A SqueezeBox or Transporter if you are reasonably computer savvy. If you aren't then you might try a DAC with a USB input. DAC1 seems to be pretty popular. Connect the USB on your computer directly to the DAC. WinAmp seems to be pretty good player for this purpose. I use EAC for ripping. DBpoweramp for editing rips is my favorite. They are both free, though DBpoweramp makes you buy an MP3 license if you are going to be creating MP3 files for your MP3 player. It is well worth it. I couldn't find another program that allows you to edit metafiles (data displayed by the media player, artist, genre etc) and batch convert files to other codecs any where near as well as this one. Plus they seem to provide very good support. That is a rarity among free programs.

I have both FLAC and MP3. FLAC for home and MP3 for portable players.
Many Thanks Regalmal! I presume that the DAC then, in turn, is plugged directly into my pre/pro with a USB to RS 232 cable. Does the Squeeze Box and Transporter perform the same function as the DAC? Puerto
Yes, the Squeezebox and Transporter both have built-in DAC's. They also permit the use of an external DAC by way of coax and Toslink digital outputs.

Puerto, the output of a DAC is analog, so it can be plugged into any analog input on your pre/pro. Another choice is to buy a USB to SPDIF convertor. The converter can have coax or Toslink digital output. You would then plug that into the appropriate digital input on your Pre/pro and so use its built in DAC. M-Audio makes a converter called the Transit that is around $100. That is a lot less than a good DAC.