Is it faster to have my old computer use the hard drive, or would a USB drive be faster for virtual memory?

Hard drive is faster than USB.

While the flash memory on a USB is faster than a HD, the USB interface is slower than HD interface.

An external drive using USB 2 would be faster than some lame internal drives.

If you’re using Firefox 4, going back to 3.6.17 might help, because Firefox 4 is already notorious for memory leaks. If they’re running both Internet Explorer and Firefox at the same time, that would use a lot of memory.

You might have a lot of software starting up when the machine boots up, that doesn’t need to run all the time, only when you want it. That would take up extra memory, too. Task Manager can show you what’s running and how much memory you’re using.

A used Pentium 4 computer (with faster DDRAM) might be cheaper than buying some RDRAM, so that’s an option, too. I’d recommend getting one that has 4 memory slots rather than 2.

I know I am goin got get some hate for this, but the only no-/low-cost way to get decent performance out of that rig would be to install Linux. There are some distros that run entirely from RAM even if you only have 128MB and that use Firefox as a default browser whereas WinXP and Win7 requires at least 1GB if you want to do anything (2GB if you want to do it decently quick). While Ubuntu has system requirements almost as steep as WinXP, that is a result of the GNOME environment; Xubuntu uses a different UI (Xfce, to be specific) and recommends 256MB RAM, though it can run on less.

So if you want speed from a low-spec system, the best way to do it is to run an OS that isn’t bloated. You can still have your Firefox, you’ll just have less overhead, and if you do need to hit up virtual memory, you’ll find that Linux handles VM better than any Windows system ever has.

@EdwinGrey USB2 probably isn’t a viable option for a computer of that vintage.

Thanks for all the advice. It’s a Pentium4, 1.7 GHz, Dell with USB2 and Firewire add-on cards.