Installing Mac Os on an external HD

livko wrote:
When I insert the Install disc in the second computer it will only allow me to install the os onto that computer's HD not the old one (which is effectively now working as an external HD).

This statement is confusing. Is the "second computer" the one with MBP's HD in it, or is it the "old one" that has that HD in it? Depending on what you mean & what the computer that is not the MPB is, you might be able to boot that computer into Target Disk Mode, connect it to the MPB, run the installer disc from the MBP to install the OS onto the drive in that computer.

A better alternative might be to buy one of the relatively inexpensive adaptors like this one or this one to temporarily attach the drive directly to the MBP, & then to install the OS onto the drive as above.

However, depending on what your original, also not specified, problem was you may have to reinstall the drive into the MPB to fully test it.

Hi livko;

I don't believe your plan is going to work for you. Since it sounds like the working Mac is not a MBP and the install setups the drivers for the hardware present during install which will be different then the MBP, if it works at all in the MBP I think it will do it only with a great number of problems if at all.

Allan

livko wrote:
The problem is that when I insert the installation disc it does not let me select the MBP drive (that shows up as as external drive) as a target for the installation...

This also isn't as clear as it could be. In what way does it not let you select the drive? Usually, you can select any drive, but some may have a yellow warning triangle next to them & selecting them results in a notice in the window about why the OS can't be installed. Do you see anything like that, or can you truly not even select the drive? If you do see the triangle, what message do you get?

Also, you still haven't described the original problem, which might provide a clue about why the OS won't install on the drive, or the model of the other Mac, which would tell us if Target Disk Mode is an option.

Something else: what type of install disc are you using? Is it a gray, model-specific one for the MBP or a black retail Leopard disc? If the gray one, you must use it with the MBP to install anything it contains on any drive. Note that you do not actually have to have a hard drive installed inside the MBP to use this kind of disc since the MBP is starting up from the installer disc & not any hard drive, internal or external.

Without knowing all the facts, I can't say if this is the best (or even an advisable) solution or not, but I suspect that you could attach the drive to the MBP using the adaptor, boot the MBP up from the installer disc, either erase or reformat the drive using Disk Utility from the "Utilities" menu of the installer, & then reinstall the OS without problems.