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If you're looking for an affordable second PC, consider purchasing a used one. For Web browsing, e-mail, word processing, and other basic PC tasks, a two- or three-year-old system can satisfy all of your needs for hundreds of dollars less than a new machine would cost.

Buying a used PC is like shopping for a used car: If you know what to look for, you can get a great value; but if you don't, you can end up with a lemon. Keep these questions in mind while shopping:

Does it meet your computing needs? Know what you want from a prospective PC and make sure it's equipped to do the job. That means looking at more than just the CPU. If you need to add hardware--a network card, for example--the PC should have an unused expansion slot and an available IRQ. (Check Windows' Device Manager for the machine's IRQ assignments.) If you plan to install software, remember that the latest programs are designed for big hard drives and fast systems. Depending on the age of the PC, you may have to install older versions of software that can run without problems.

The performance boost you'll get from a CPU upgrade rarely justifies the cost, but adding memory to your system is often worthwhile. If you expect to add a graphics board or sound card, make sure the PC's motherboard will accept one; some budget Celeron-based systems with graphics and sound integrated on the motherboard will not. Check the documentation.

Does it have documentation and program/system disks? A manual covering the PC's motherboard is essential. Without a manual, you won't know how to change jumpers, the BIOS, and other motherboard configuration settings. For example, adding a faster graphics card to a system that uses an integrated graphics chip may require that you disable the on-board chip by changing a jumper before you insert the new card. Likewise, you may need to adjust a jumper setting before flashing your BIOS or replacing the CMOS battery on the motherboard.

To install or reinstall drivers for graphics cards, printers, and other devices, you'll need the Windows CD-ROM.

How clean is it? Pop a key off the keyboard with the end of a pen or pencil and take a good look at what's underneath to get an indication of the PC's environmental history. If you see lots of sand, dust, and potato chip crumbs, pass. Avoid a PC with dust-clogged fans and vents, or significant amounts of dust inside the case. A poorly ventilated case means the PC has probably been running hot.

How well does it work? If a used system is working well when you first get it, there's a good chance it will continue to run well for quite a while. Still, it pays to thoroughly test every component in the PC before the purchase.

The biggest question in evaluating a used PC is its hard drive. You may be able to spot imminent disk trouble by running ScanDisk in Windows 98 and Me (click Start, Programs, Accessories, System Tools) or Error-checking in Windows 2000 and XP (open My Computer, right-click the hard drive, and select Properties, Tools).

Finally, run TuffTest or another comprehensive diagnostic program. You can go to our Downloads library to get the free Lite version of TuffTest, but I recommend spending $10 for the full version of the program. The complete program thoroughly tests all key hardware components and issues reports. It also runs from a bootable floppy.