Closing TCP/UDP Ports on Server & Clients?

[CJarman]

We recently did some Nessus testing on our domain. We found that some unused TCP & UDP ports were open -- nothing major.

I have two questions:
1) Do we NEED to close these ports (ie TCP 137/138, UDP 445, etc) as Nessus results suggested?
2) If so, I would like to close those ports on both our servers and client PCs. We use Win2K Server and have a mixed client environment of Win98, Win2K Pro and WinXP Pro. One possibly important point to note is that NOT ALL of our client PCs are actually connecting to the domain network, though most have access to email and/or Internet. Is there an online or offline resource that will explain the steps in high school language? I ask for high school language instructions because I'm not a long time network admin. I'm essentially a long time hardware guy who has recently taken on the position of Sys.Admin, so step-by-step instructions would be MOST helpful.

BTW, I have read about using IPSec. If memory serves, that won't work correctly in our environment because of all the mixed OSes. Am I wrong?

THANKS for any help you can offer...
CharlieJ

~Not perfect, but forgiven~