If you're shopping for a machine for business, you might be encouraged to get Microsoft Windows 2000 instead of Windows 98 or Windows Me, which are marketed for home use. Although Windows 2000 is more robust and reliable than Windows 98 or Me, it really isn't necessary for running business applications that also can run on the consumer versions of Windows. I like Windows 2000, but I also like Windows 98 Second Edition. I recommend a minimum of 20 gigabytes, but you'll find that 40 GB isn't much more expensive. If you have an older machine, you can add memory and a second hard drive.
Memory is now very cheap.
Check with your PC manufacturer to make sure you get memory that meets your machine's specifications. I've always recommended a backup system. In the past, I suggested either a tape backup or a Zip drive. But they are no longer needed because you can now back up to CD-ROMs. In the old days, I recommended a modem on every machine, but today that's not necessary if you have a broadband connection such as digital subscriber line or a cable modem and a local area network, or LAN, to connect you to the Internet.