Hi jaquie,
This is what the forum is for. I too would be stumped if it wasn't for all the generous people out there willing to give their precious time.
The laser itself will work from an old 386 computer but you will need a fairly fast one if you are going to do design work as well as running the machine so I suggest get the fastest one you can afford. Anything over 2 GHz (gigahertz) would be satisfactory. Athlon, Celeron, Pentium etc will all run the same software and the only difference is stuff like larger on board cache memory or maths floating point co-processor on the chip which shouldn't be needed unless you are running very graphics intensive stuff like 3D games or 3D drawing programs. The chips are so cheap now that you should just get the fastest one you can afford.
Check out www.Dell.com as they have some very cheap NEW computers and you can mix and match what you want in them and also get a good warranty period and also the latest fast computer (I don't think you need the duo core or 64 bit chips though. Just a single core 32 bit chip will do). Sometimes they have a special on computers and a basic one starts at $459 with monitor.
If you already have a monitor, don't buy one. Same as a keyboard, mouse, system box, power supply or any peripherals you may already have but as you said you are a Mac person so you or your friends probably won't have these laying around. Over the past 4 years my friends have been looking out for computers for me as they know I use them fairly often in my hobby so now I have about 7 of them and LOTS of peripherals and can mix and match some parts and build some workable machines out of them.
Get the largest hard disk you can afford as it will be where you store everything that you will be doing. Your files will build up as you go and if you are sentimental about old stuff then you won't delete many, if any, files as you gain more experience. I wouldn't get anything under 120 Gig. ($109.00 AUD) Also partition the drive into 2 different partitions and save all your work on the second one because if anything happens to the C: partition then all your files will be ok on the D: partition if you have to reformat the drive through a corruption like a virus etc. I know this from experience. Also a backup program is essential if you don't want to lose any data. Ask at your local computer store for which one is good and easy to use as there are many out there and some even free. You can even play music on the computer while you work if you haven't a radio close by.
Also try to find a card reader to put in it as heaps of people use these things now and they are extremely good for transferring files from one place to another. In the winter months I design work inside the house where it is warmer and transfer my files to the machine in the shed this way using the flash drive. I have 1 Gig for $32 AUD (cheap) 1 Meg files take about 2 secs to download. I used to use a CDRom drive but found it way too slow compared to Flash drives.
All I can think of for now but keep the questions coming as it just doesn't help you.....it helps everyone out there interested in starting up (and we all had to start somewhere).
Now. Have you got a wiring schematic in ENGLISH for my Chinese laser power supply ???
warm regards
Rich.