older mac pro

i have a 2006 mac pro, osx 10.7.5. i'm finding i cannot run some of the newer photo software that i would like to try. i'm not very tech savvy and am wondering how the new mac mini would compare performance wise.

Compare here:
Home - Geekbench Browser
(Browse results, search for MacPro, MacMini, etc)
Your Mac Pro is a MacPro1,1 with a multi-core score of 3500-5000
Mac mini7,1 (i5, 2.6GHz) has multi-core score around 6500
cheapest model (i5, 1.4 GHz) has multi-core score around 5400.

HTH

Of course, not everything revolves around the processor, so there are other factors to consider, like the graphics setup and how much RAM and capacity and so forth, but yes processor speeds have improved a lot since 2006 and with SSD the speed of general operations has likewise gotten tremendously faster if you want to go that route.

If you wanted to spend money on the Mac Pro, an SSD in Bay One with the System Software on it and say an ATI Radeon 5770/5870 Mc Pro graphics card would improve things greatly. The old original 7300 is pretty slow.

even if i could put mountain lion on it would be great. but i don't think that's possible?

Well it may be if you make a hackintosh of your lovely Mac Pro, but be aware it sometimes happens a hack turns into an expensive door stopper. Google will help you find the hacks.