Ok so I'm going to be retrofitting a Mori SL1 lathe.

I guess what should I use? Mach 3 or a standalone controller with it's own software and interface?

I already have multiple machines running mach 3 and i like it.

What would i Need to Run Mach now, my old machines are mach 3 with a computer holding onto XP. Nothing new allows xp to be installed as far as I know, the drivers are just not made.

So if I go 32bit Windows 7 what BOB should I use with my new servos? And will it run windows 7 effectively? I'm not convinced that Mach 4 will do everything Mach 3 will, yet.

Also how do I control the other items such as automatic tool changer?

If the old amps/drives are working then I think I would keep them. They will almost certainly be analogue command so I would  get one of the controllers capable of outputting +/- 10v .
There are a few, the one I use is the CSMIO/IP-A but there is also the DSPMC, Galil and Kflop with Kanalog.

Toolchangers can be done from VB using the I/O from the controllers mentioned above or using a PLC. I use a PLC on my lathe and VMC for two reasons, first I had them already, second I am better at ladder logic than VB script.

Hood

If I'm going with new servos, does it really matter which motion controller I go with? There are so many options. I would like to use the old servos, but I'm leery of using them because I'd have to figure out how to wire them and figure out how to use the index pulse.