I have a Mac G4 running OS 10.2 with USB peripherals. I want to use
these peripherals (monitor, keyboard and mouse)  with an additional
Dell PC with serial ports. I know that I need  a KVM switch to do this
and would like to know the best configuration to solve the problem. I
also don't have a lot of  money to spend on this.

Hello:

I am not a prescreened Google answer provider but I saw this question
and couldn't resist.  I also use a Mac but am still stuck in OS 9.2. 
However, I frequently use OS X for various purposes.  Now to my point:
I recently setup a Linux system and from my OS 9.2 system I access it
fine through a program called MacSSH.  But, of course, that only
allows for command line interaction.  However, depending on the OS on
your Dell (i.e. Windows 2000) you should be able to access it in real
time while booted in OS X - kind of like Virtual PC in that it would
be open in a window with OS X in the background.  The upside to this
is that no KVM would be needed.  The downside is that the PC would be
a bit less responsive than if you used a KVM.  So if you don't use the
PC very often and it is a Windows NT, 2000, or XP system I think it
would work fine.  If you are OK with going without a KVM, I can tell
you how to open that Windows 2000 system in a window while booted into
Mac OS X.

The cheapest way to go is to buy a USB card for your Dell PC. You can
get these for as little as $10, sometimes even free after a rebate. If
your Dell has a reasonable amount of life in it, you might consider a
USB Version 2.0 card (faster) for a little more money, which is
backward compatible with USB 1.1 peripherals like a typical KVM
switch.
Once you have your USB KVM switch and the USB card in the Dell, almost
all USB keyboards and mice will work on both the Mac and the Dell.

2nd best is to get a P/S2 KEYBOARD-to-USB INPUT adapter
(unfortunately, much more rare then a USB KEYBOARD-to-P/S2 INPUT
adapter). Then, you can use your original Dell Keyboard and a P/S 2
KVM switch on your mac. Unfortunately, the only place I know to get
this P/S2-USB adapter is with the old (P/S 2) Microsoft Ergonomic
Keyboard with USB adapter. $39 at Fry's.