If you really want to give Mac OSX a try, here's some resources!
First, full tech specs for your machine:
https://everymac.com/ultimate-mac-looku ... ords=a1224 .It looks like you'll want 667 MHz PC2-5300 DDR2 SDRAM 200-pin SODIMMs. Stick with whatever's cheapest on ebay/amazon.
Don't waste time upgrading the internal drive - Mac OSX boots quite well from an external drive. Get a firewire800 enclosure, since they're dirt cheap now and a lot faster than USB2. The one I had for my 2009 Mac Pro is
out of stock from the ebay seller, but you can find
a listing here. More discussion here:
https://discussions.apple.com/thread/8375840 Pair that with a cheapish SATA SSD and you're good to go!
Here's a direct download link to El Capitan:
https://support.apple.com/en-us/HT206886 - download it, run it, and set your external drive as the install target. When it reboots, set your external drive as the default startup disk. Easy peasy!
If you want to try getting newer Mac OS versions to work, there's usually someone hacking away at that stuff on the macrumors forum. Look for threads with titles like
mojave on supported macs. I stopped going to the macrumors forums because it's full of weirdos, but it's got useful info for older macs.
If you eventually throw windows on there, you can do a direct install and use
brigadier to get the relevant Boot Camp drivers directly.
Also, if you really want the full Mac OSX experience, consider getting a
magic trackpad. It's eye-opening how much better
gesture navigation is in Mac OSX compared to windows (barring Win10+precision trackpads). But full disclosure, it only works as a basic trackpad in Windows (left/right click and vertical scrolling only).