Chris, following advice received from ADS & co, i've recently invested in moving my CD Collection to laptop for paractical purposes, and despite my earlier reservations I've come to the conclusion, even this early on, that it's the best thing i've ever done
I'm using a 2nd hand SONY VAIO. Spec:- 700mhz p3 Processor, 128mb Memory (in the process of upgrading to 196mb which is the limit on this model - although currently running smoothly on 128mb) 20GB hard drive. Running OTS DJ on a single integrated Soundcard. I chose the VAIO since it has a good reputation for multimedia applications, and despite advice against using a laptop soundcard for this application, I honestly can't find any degradation in sound quality when plugged through a 3kw PA

. Paid £320 from E-bay for the machine, and just formatted the drive and re-installed the O/S (Win98SE) and drivers. I don't run any other software on the machine other than Win & OTS or allow it connection to the 'net, I rip the CD's to OTS files directly from the main pc and transfer to the laptop using a 10/100 network connection.
I also bought a faster IBM Celeron 1.2ghz as back up (20gb/ 128mb/ Win XP), thinking that the VAIO wouldn't be fast enough (Wrong!), but i'm happier running the VAIO as the main machine and so far it has run glitch free and the audio is a little bit better on the VAIO.
I believe that OTS can run on machines P2 266mhz and above, although I would consider perhaps using 256mb+ of RAM on lower spec machines. Certainly 400mhz seems to be what a lot of D.J's are happily using at the moment.