Does my mac pro 1,1 support 64-bit OS???

It supports a 64-bit OS and runs 64-bit applications, but it cannot boot the 64-bit kernel, hence, if will not run Mountain Lion, but it will run Lion. But Lion will be the end of the line for first generation Mac Pros.

In order to boot the 64-bit kernel of OS X a computer must have a 64-bit EFI boot ROM. Your Mac Pro only has a 32-bit EFI boot ROM, hence, it cannot boot the 64-bit kernel.

You can boot Lion. You cannot install and boot Windows 7 64-bit, but you can use the 32-bit versions.

Drivers and especially graphic drivers, really do need to be full 64-bit.

Even booting (or rather installing, as booting is 100% fine) is a problem with Windows 7 Pro 64-bit.

The oldest OS it can use is the OEM not retail of Tiger 10.4.6, it can run 10.7.4

You do not technically need UEFI, the EFI64 part, but that is what has been done.

I would not nor would I get a 2008 model either (which will support ML, but there are too many symptoms of age I think lately) unless you are fine with 10.6.8 which it will run nicely.

Depends on why, the price.

It will take more memory but after 8 x 2GB it gets too expensive. It probably needs a new graphic card.

You mis-read Everymac.

The use of 32-bit Windows was... terrible, because then you only get support for mere 1.9GB RAM - due to old EFI32 (which was baked in 2005 and the 2007 EFI update made booting Windows slower but "added compatibility" - never saw that extra 30 seconds as better.

I looked and did not say anything about XP etc. I can tell you from 6 yrs owning one. And I dont' want to when you could have linked to THIS Mac Pro or there is Apple's list of supported--- which we take with a grain of salt and even unsupported manage to install.

Get a PC or a 2009 Mac Pro - Apple Stoe Specials $1900 has the 2010 4-core 2.8GHz which is a much better machine and easier to use plus good investment.

It is harder to burn the DVD again with Imgburn so you can boot the install DVD for Windows.

Or install on a PC - don't let it restart and continue, shutdown and 'sneaker net" the ahrd drive to the Mac.

It isn't worth it.

64-bit Windows shows all the RAM - you need Windows 7 Pro to use both processors, and 64-bit support. Home Premium is one processor and up to 16GB RAM. All of that is online.