Thanks samantha23, have no problem using XP or Vista but getting a 32bit PC is almost next to impossible so I decided to buy the UC100 motion controller as you can see from my previous posts on this thread.

Recommend 32 bit, on XP rather than Vista, with parallel breakout board.
If you are using an external motion controller, then Mach3 will run on 64 bit, but may not function fully in all areas, for instance, closed loop control that passes through mach3 may encounter issues where mach3 ignores signals that it would ordinarily have detected in parallel operation.
The old setup with the legacy printer ports seems to be the most reliable and robust, and is generally more affordable than good quality USB or LAN motion controllers.

When looking for old computers, I recommend using the keyword "refurbished" in your search terms as these are cheeper and more abundant than trying to track down a legacy motherboard.
Just make sure you get one with the big, pink/purple parallel port on the back, some retailers don't even know what they are since they are so outdated, so you may have to ask them specifically if it has that type of port on it.

The only place I can buy refurbished 32bit old pc's is Amazon or eBay but the shipping cost is expensive and not even sure if I get a 32bit pc. For now my UC100 may work good but in the future I will consider upgrade to Mach4

As to whether your PC is 32 bit or 64 bit depends entirely on whether you personally choose to install windows in X86 or X64 on it.
Look for something with a celeron, Core2 duo or early I series processor.
A Dell Optiplex or one of those old slimline Mecer office boxes for example make excellent CNC controllers.
They are the type of computer Mach3 was originally coded to integrate with.

They are so cheep I'd recommend buying a backup one at the same time.

I recently bought Optiplex 780 boxes for 1000 ZAR, which is about $50 each.

From here, you can simply install Windows XP on it and configure it for X86(32 bit mode.)
32 bit or 64 bit is not hard wired into PCs from before Windows 8, you have the option to choose.

The units available on Amazon are probably among the best choices available to you when trying to set up Mach 3 the easy way.
But you will likely need to phone the sellers and ask about the parallel port since most simply post a photo of the front of the tower and expect customers to be satisfied with that.

If you find out, a little down the line, that the UC100 isn't performing as you'd hoped, I'd definitely recommend taking this route as it is the most trouble-free.