If you only use PhotoshopCS3e, Artezin and Lightroom on this system, why use Vista? Most of the benefits in Vista won't affect any of these programs. If you use XP instead you already saved a few 100MB more than you can gain by turning off all services. Do understand that most of these services are covered by "mysterious clouds", meaning that it's not often very clear what the purpose of a particular service is and what negative effects you could experience when you turn it off (many services have more than just a single purpose and some depend on each other). Also the system might run perfectly fine with a few services off, but future installations of other applications or updates might lead to very confusing errors that are caused by some default services turned off. The question remains; will the user think months from now when he has some strange error that it might be related to a disabled service or will he have forgotten all about it and pull his hairs out for days, if not weeks?
I have the advantage that I've been an application programmer for several years, so I know how programmers think, act and what common mistakes they make. One program in which the programmer assumes that default service X is running, could lead to crashes or errors. Again, this is a good example that OS stability can be really affected by poor application programming. My advice is always; stick to defaults on your system as much as possible and not only with services if you want to avoid strange problems (in any OS). Change for example the size of your system fonts being used by your OS (like the ones being used for menus). Sounds innocent, right? You'll be surprised in some cases.
Do understand that 2GB is not the limit for 32 bit systems. You could get close to 3GB, but it all depends on the hardware you use. The point is that the maximum amount of memory that can be addressed is 4GB (2^32), but this includes things like memory on your video card and all other expansions. So if you would use 512MB video memory, then you're already at the limit of 3.5GB and that doesn't include all the other hardware that needs memory space.
The other option is of course to go for Vista or XP in 64 bit, although I have little experience with that, I also don't know whether the programs you mention can fully utilize the extra memory address space.
But if you want to stick to what you have now, then feel free to look at a site like this::
http://www.blackviper.com/WinVista/servicecfg.htm
