The short answer is go with Vista Home Prem 64bit.
Vista is hard on your system resources, mainly memory & hard drive space, but inspite of this it's actual very quick. Turn off the user account control and it's livable for day to day use. Memory is dirt cheap these day even for the good stuff, just slap in 2gb and that side of things is fixed, HDD space is equally cheap these days just allow 20gb for Vista, 15gb for the basic install and another 5gb for drivers, applications, and running space. There are any number of services etc that can be disable or removed to slim things down. The only thing I'd really also suggetst is make sure you graphics is areo compatible not that you likely to ever use it.
Since that basically a list of what wrong with Vista why use it:
- It cheaper: you can buy Vista Home Premium 64bit cheaper than you can Windows XP Pro 64bit. (Of course there are pirate copies of both available)
- It easier to get: alot of places will look at you blankly if you ask for XP Pro 64bit, Vista 64bit is easily found in almost all computer outlets.
- Drivers: this is the big one, Vista 64bit has good driver support for most system harware, and average driver suipport periphals. both will only improve with time, XP 64bit on the other hand was basically still born and as such has only average driver support for system harware, and rubbish support for periphals.
- General Support: Vista is new and while most people don't like it support for it will only increase over time, XP 64bit is very little support and that will only get worse with time.
The only problem I've seen to date with running Vista 64bit in a MAME cabinet is avialablity of lightgun drivers, but this is more of a 64bit OS problem than just a Vista problem.
Just a side note, Window XP 64bit is not a hack, it is a fully 64bit OS, the only catch is for compatiblity & developemeht reasons it still has a number of hidden limitations left over from the 32bit version. These limitation were removed in Vista 64bit but they are unlikely to have any effect on MAME either way.
Please note I'm not a Vista lover, I run XP Pro for 95% of my day to day stuff, and Vista Ultimate 64bit for MAME and a few other things that gain noticably from the 64bit Enviroment. I still cannot suggest anyone in business use anything but Windows XP Pro, unless they are using high resource apps like CAD.
I've also TRIED to run SDLMAME on 64bit Linux, but as linux feels like Windows 3.11 with pretty graphics and an Internet connect, and it's hardware compitablity is rubbish in my book, I can't suggest you go the route either. I tried three different distros and two wouldn't even install on my Core 2 Duo (they isntall on my Athlon64 x2) and one that installed but was useless and crashed and died two days after it was installed.