I have room for another one, and I have a spare monitor! Want my address?

You can buy a switch to plug both computers on the same monitor.

It's possible to have multiple monitors on one computer. Is there any reason why you can't have multiple computers with one monitor?

(At the same time I mean.)

At the same time no. But as I mentioned and as c242 mentioned too, it's possible to buy a switch for the monitor. Turn the switch to use one computer or the other with the monitor. Since it's a Mac and a PC computer, I doubt you'll get the mouse and keyboard to work with both though. But the monitor will be no problem with G3's and more recent monitors. (older Macs used a proprietory cable for the monitor, but recent ones use the same as the PCs)

Ryan...I doubt it...two cards driving the one monitor would play havoc with refresh rates, etc...and be bound to blow the hardware....like trying to engage two gears in your car at the same time...

OK, after a quick search I did find some USB switches. I didn't think they made those. The ones I've seen in store were all PS/2.
Search for "KVM switch" (stands for "Keyboard, Video, Mouse") in your favorite online store, or check out this site: http://www.kvm-switches-online.com

Yes! switching using the same 'input/output/ devices it's a good idea!

-I will purchase a new monitor (to get best refresh rate), and i can get a USB monitor. Now, i'm also using Linux OS, so i need to check first if this kind of monitors are covered by Linux. If not, i can purchase a Monitor Switcher (2 VGA cables to 1 output monitor cable).

-About the mouse there's no problem, i have a USB mousse that works fine in booth platforms without configure it.

-About speakers, there's also no problem, booth computers have sound out connection. The G3 have also one speaker incorporated (not sounds very fine, but it sounds).

-The major problem is the KEYBOARD. On Macs you can only connect Mac Keyboards! It happens the same on Windows. So i need to get space for two keyboards.

Mmmmm, if the problem it's only with the keyboard, i can put the two computers over my work table, and i will get a small net on my home!

Thanks for the Switching suggestions

I checked the USB Apple keyboard just before i post my last comment, and don't works in WIndowsXP. But i can search if there's any driver for WInXP; it will reduce the USB mouse and keyboard connections to only one USB connection (Mac keyboards have two USB connections). Now the 'smalls' problem it's: wich is the function of 'command/apple' key in WIndows? If there's a solution to make this key as a 'Windows Ctrl' it will make my life much easier (comd/apple key is in Win 'ALt' position)!
My keyboard is the first Apple USB keyboard not the Apple Pro keyboard. The differences are: exclusions (on my keyboard) of 'Del', 'Open CD' and sound controls.
Let me know if there's a possibility to use my Apple keyboard on WindowsXP, Nikos!

ok. My USB entrance that i used at first atempt do-t work. Now i connected the USB Apple keyboard and works!