Newer computers usually have four or six sockets, but whether they have more than one logical port is sort of "iffy." It's fairly common to have two ports, with a socket for each front and back. It's also fairly common to have two connectors front on one port, and two back on a second port. I haven't had hands-on with a 6-socket to see what they're doing there, and the specs don't tell me.
On my own machine, since I plugged the dongle for a wireless mouse in one of the front sockets, using the second front socket to download from my camera sometimes makes the mouse "twitchy," so I sort of have assumed both front connectors are on the same port.
Theoretically, a single hub should be able to handle the logical connection of multiple devices, but early USB hubs - like what's probably inside an older computer - sometimes do poorly. The power drawn for the external devices may be the real source of the problems, especially when more than device at a time is used.
I use one of my two rear USB connectors into a Belkin 4-port (with wall-wart power) with a printer, scanner, and one hard drive permanently online through the Belkin. The fourth output from that Belkin goes to a newer (and cheaper, but also powered) 6-port that I use for things "occasionally connected," such as a couple of cameras, an "occasional use" inkjet, and two or three backup hard drives that I hook up only while backups (or restores) are being made.
Once all the little boxes are isolated from the built-in hub through good quality powered external hubs, I don't have any problems; but as noted, plugging a third device directly into my computer is sort of a marginal exercise. (It is a fairly old computer, so newer ones may have better capacities.)
You should get similar performance with Win98, but you will probably have to install drivers on the computer for any hubs and for any USB devices you attach. Win2K and WinXP do it automagically so you don't have to fuss with driver disks. Limited experience indicates that "automatic mounting" of USB devices may also be one of the few things they didn't screw up in Vista.