I haven't used an Apple comp since 1984,  but I'm getting a Pro Tools system
from a co-worker,  along with a Mac.  He says it's a bit old, and not all
that powerful,  so I'm considering seeing what it would take to upgrade it..
so that brings on the questions...
Obviously, I do know that the processors are different,  but what about RAM,
or hard drives? Do Mac's require a different type of RAM,  or will they use
the same as PC's?  Same question regarding hard drives... etc..
Thanks........
Recent Macs use the same types of RAM and drive connections as PCs, but 
that's not true of many older ones: it depends on just how old. If it's 
a G4-based system it'll have ATA drives, PCI card slots, USB (& 
FireWire) connections, &c., but if it's a first- or second-generation 
PowerPC system it'll have SCSI drives, NuBus slots, proprietary ADB & 
serial ports, &c. G3 systems are transitional; industry-standard 
components were 'swapped in' incrementally over the life of the 
product-line, from the beige 233-MHz systems to the blue-&-translucent 
300- & 400-MHz minitowers.
If you can find out the exact model it'll be possible to be more 
specific about its components. If it's in running condition and has OS 
8.x or later, maybe you could ask your co-worker to print out or e-mail 
you the hardware & peripherals reports from the Apple System Profiler 
program (usually available from the Apple menu); this will give details 
of the CPU & motherboard models, installed RAM, drive connections, &c.
What's Pro Tools, BTW?
-- 
Odysseus
Short answer-- it depends.
Find out and repost with the model name... and you can get a more 
specific answer.
However, in general, any Mac from the past 10 years or so will probably 
use generic PC RAM from the same era and standard IDE drives.
Not every CD-RW or DVD-RW model will work with Mac software, even though 
they may be physically compatible with your Mac... but standard IDE hard 
drives should not be a problem.
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If your gifted mac is too old, considering upgarde pricing and performance 
issues you might look, instead, at the Mac Mini.  I've got one now attached 
to my PC network and KVM'd with my XP machine.