Jordan, have a look at
SmoothWall. Their product requires a low-spec PC (like a Pentium 100, and 128MB RAM with a 10GB disk, two network cards) and turns it into a firewall appliance. There is a free version and a commercial version. The commercial version can be specified with plugins that really lift it up towards the Cisco PIXs and Nokia/Checkpoints of this world.
Also, if you're not averse to spending some money, you can get the excellent Cisco PIX 501 for $375 from NewEgg (
linky) .
This gives you a 10-user license and VPN support. It's the PIX-501-BUN-K9 package. You probably don't need to be hosting your own VPNs so see if you can find the PIX-501 package. More info from Cisco
here.
The reason I suggest this in preference to installing a software firewall (even an appliance like SmoothWall) onto your laptop is twofold. Firstly, you need two network cards (public & private), which will need you to fit at least one PCMCIA network card, and which is likely to cause the laptop some problems.
Secondly - and more importantly - laptops are not designed for 100% 24x7 uptime, especially not ageing ones. If you buy an appliance like the PIX, it is designed to be up all the time. Yes, config can be scary to start with, but it's all quite logical, and for a £300 box, it offers a lot of flexibility. I've put several of them in, and they're excellent.
If you decide that a hardware firewall is the way to go, please please please don't get the Nokia IP40. It's awful.