Microsoft hasn't supported Windows 98 for several years now. Any computer from that era would probably never have enough horsepower to run eCabinets.
Take Dickey's advice and shop for a new computer. Before you do though, make sure you check Thermwood's Recommended System for eCabinets.
You can find great deals on very capable workstation-class computers at the Dell Outlet.
Whatever vendor you decide to buy from, make sure you buy a WORKSTATION-CLASS computer. Anything less may run eCabinets but it will likely be painfully slow with plenty of crashes along the way. This means stay away from Wal-Mart, Circuit City, Best Buy, Office Depot, Staples, etc. They only sell consumer-class home computers that are not suited for eCabinets.
As Dan said, and some further elaboration. While most "consumer grade" PC's could run eCabinet Systems, albeit marginally, there are 2 things to consider. One is they are almost preinstalled with Windows Vista. I won't share my personal opinions on this OS, but needless to say, eCabinet Systems is not certified to be used with Vista.
Second, while most share many components with the more "industrial" grade peers, the power supplies usually are not robust enough to support max memory, expansion graphics and a fully tasked processor for long. 350 to 500 watts is what I say is a minimum steady output requirement. Along those lines, most of these "store bought" PC's have "integrated graphics". This means that the video part of the computer is "built in" to the main board. Usually this means that there's not a "dedicated channel" for the graphics. This is acceptable for home use, but ask any gamer or CAD user - you really do need a separate and powerful graphics card (in a way, eCabinets can be thought of as a state-of-the-art video game as well as a 3-D CAD package...).
I have at home, as my primary PC, a Dell that I had built to eCabinet Systems specifications, that dual boots Linux and XP, has full multimedia capabilities and it cost under $800. Add a monitor and printer and for about a "kilobuck" you will have PC that will last for years, can be upgraded, and can be relied on for fun and work.
One final thought - always remember to back up your work - even the best PC can fail or get stolen (or whatever) and if all of your work is on it, you don't want to have to start from scratch, do you? Your old Win98SE (yes, unsupported, but still well maintained by many enthusiasts) would make a great back-up machine for your data.
Another thing to keep in mind that Windows 98 has a 2GB disk partition size, effectively limiting maximum file sizes to a bit less than 2GB. This could make using it for backups difficult if you were to backup the entire hard drive.