There is a second alternative to VMware (and slightly less expensive).
Virtual PC by Connectix works essentially the same as VMware.
I have successfully installed RedHat 7.1. Your mileage may vary depending on the distribution you choose to install.
Virtual PC solves potential hardware compatibility problems by emulating a given set of hardware across all software platformas installed regardless of what actual hardware you have installed. This mainly affects such hardware as video and audio. The latest version of Virtual PC (4.3) will accept versions of Windows 98SE or later for the host operating system.
An added benefit of Virtual PC (don't know if VMware includes this capability) is the ability to create a virtual network among installed virtual computers. This virtual network can also interact with a physical network. The would allow the following:
Windows 98SE host operating system connected to a NT4 network. Windows 2000 Pro, Windows NT4 Workstation and Red Hat Linux 7.1 are installed as 3 virtual PCs. If the Win 98 computer is robust enough (powerful CPU and losts of memory), you could start all 3 virtual PCs and connect them (along with your Win 98 PC) to your NT4 network.