Toshiba Tecra S1: Harddrive Replacement Help

So I am over at my sister's place Friday night and she asked me if I would like a laptop. I said sure, let me take a look. It is an old Toshiba Tecra S1 (from about 2003) that she got from work and it is actually in decent shape (for a company work laptop that has been passed on to several employees) and solidly built. I have fiddled around with it for 2 days and suprisingly it is very stable.

It has the latest BIOS (from 2005) and I was able to upgrade the Intel wireless driver that was dated from 2006. All USB ports are working (unfortunately no S-Video or Firewire). It has Windows XP Pro and I was able to install SP2 without a hitch. The cpu is a 1.4 GHz Pentium M. It also has a DVDE/CD-RW drive.

The only thing that I see as a drawback (besides old tech) is that the harddrive is a mere 40 GBs. I know very little about laptop hardware except the basics so can anyone suggest what harddrive I should consider as a possible upgrade? I have done research but as I said I am pretty much a noob concerning laptop hardware especially older offerings.

I have researched and I do know it is an IDE drive but will ATA-6 drives work as a substitution? What do I need to know/keep in mind?

Thanks.

For IDE/P-ATA, in my opinion, you want to target Seagate's 5400.3 line. 5 year warranty (or there abouts depending on where and when you get it) and pretty decent speed. They max out at 160 GB. For best performance, target the 80 or 160 GB capacities.