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Do you have processor envy? A CPU upgrade can satisfy your power lust, boosting your Pentium, Pentium MMX, or K6 CPU to between 333 and 400 MHz.

Most upgrade kits use the AMD K6-2 processor and cost between $150 and $200. And an older (up to 333-MHz) Pentium II system can be upgraded to 400 or 500 MHz with one of Evergreen Technologies' Performa upgrades, which use Celeron chips and sell for $130 to $230. Finally, if your Pentium II is fairly new (about 18 months or less) and your motherboard is compatible, you could upgrade to a new Pentium III, such as a PIII-500 (about $250) or a PIII-600 ($500).

As PC prices fall, consider whether upgrading the CPU is worth it. Usually, you can expect only about a 25 percent overall improvement when you upgrade an old PC. Getting more requires upgrading other components, like the hard drive.

If you can't double a system's speed, a CPU upgrade probably isn't worthwhile. Further, if the cost exceeds 75 percent of the price of a new system, buy a new PC.

If you decide to upgrade, do two things first: Back up your hard drive and check that your PC's BIOS is up to date (see the upgrade maker's Web site).