I'm new to Linux, and need to use RHEL 3.0 for a legacy prog.
I'm using a MacBook Pro 17" and apart from the difficult triple boot problem (rEFIt helps here), I can't get past installation because the install doesn't recognise the drive: is my hardware too new. Is there a driver out there? I've searched extensively and not found anything so it makes me think I'm barking up the wrong tree.

More than likely. I don't know much about Apple except that they preferred ATA drives until recently. I wouldn't be surprised if they now use SATA drives too, which Linux has supported on a wide scale for only about a year. So: you'll need to find a driver for your chipset and install it manually. Or install something like vmware and then run RH3 from there; no problem since vm can emulate ATA. On top of that, no fussing with double or triple boots, you can run it all from one OS. But you'll need enough RAM, of course.

S-ATA confirmed. I actually had alot more "joy" using virtualisation (Parallels) because that just presented a generic disk controller to the install. Only thing is, the USB support for virtualisation is something of a compromise, so I managed to fundamentally impair the virtual machine OS simply by plugging in a pendrive... not good.

As I am a newbie, can I ask a first principles set of questions? Background is that RHEL3 is specified for a piece of software (MRI control), but the hardware is not available anymore.
What is my best option?
- try a different flavour of linux
- dig about for S-ATA (and other) drivers
- virtualisation (but try a different virt solution)
- others?

I would be surprised if your applications didn't run on a more recent version. SATA should be well supported by Red Hat 5 and its community (free) clone CentOS (I'm being tentative here as Red Hat lags about a year behind the mainstream). One distro that is closely related to Red Hat is Fedora and it definitely has good SATA support by now but it also sits on the cutting edge so it is not necessarily the most stable one. I haven't experienced any issues yet, however. Fedora is free just like CentOS so the worst you risk is wasting half an hour of your time.

VMware tends to run Linux clients very well but the range of possibilities is rather limited if the host is a Mac. There is a commercial vmware solution (VMWare Fusion) but I'm not sure whether it supports Linux at all.

Installing new drivers will be challenging, to say, the least. It would be a lot easier if you could get RH to install at least partially but if not, you're doomed to installing and recompiling on a different machine or manually editing the iso.

I really appreciate your help, I hadn't understood that drivers involved recompiling the source and creating own install CDs - owch.

I think VMWare Fusion does support Linux and ~60 OSs. I'll try that too.

The vendors of the software I'd like to run specify that RHEL3 and 4, and the need to install every package.
- Am I right that this involves a current subscription with RHN (I'm on evaluation subscription at present).
- Given their stringent line on this, I'm hesitant about CentOS. Still go for it?

Installing drivers can be a lot easier than, in fact, but in your case you are looking at a vicious circle: you need the driver to install the OS but you also need the OS to compile the driver. All you can do in that case is directly edit the iso or compile the driver on another machine.

Yes, Red Hat requires a subscription. Bear in mind that support is limited to three years so Red Hat 3 must be unsupported by now. RH4 should still be supported but I imagine that they would much rather see new customers adopt RH5.

I wouldn't worry overly much about CentOS. It is essentially the same product. What RH makes you pay for is not so much the software as support on that software. If you need technical assistance, then you should prefer Red Hat. If you think you can cope, you could use either.