As to how "efficient" UNIX is, it totally depends on your preception. If "efficiency" for you includes "does it run ALL my current Windows applications without much fiddling", then it's probably not very efficient.
As regards the system requirements: That depende on what flavour and version of UNIX you choose. For NetBSD e.g., requirements can be VERY low:
Quote:
The mini-mal configuration is said to require 4 MB of RAM and 50 MB of disk space,
though we do not know of anyone running with a system quite this minimal
today. To install the entire system requires much more disk space (the
unpacked binary distribution, without sources, requires at least 65 MB
without counting space needed for swap space, etc), and to run X or com-
pile the system, more RAM is recommended.
That is not to say that UNIX was only for old computers. It you throw top of the line hardware at it, chances are you'll get unrivalled performance out of it.
Without having any actual hands on experience as regards your scenario, here's what I would do in your case:
1. Back up all partitions, just for good measure.
2. Convert or reformat the 20 GB partition to FAT32 (if applicable).
3. Shrink that partition to 10 GB. This 10 GB FAT32 partition will be your jointly accessible storage volume, i.e. all your operating systems will be able to access it. (There are tools out there that can do all of these things, but I don't know them offhand. Google for them or ask specific questions in these forums.)
4. Create a new partition on the remaining 10 GB and format it ext2 or something else (whatever filesystem the flavour of UNIX you're installing supports best). It is, I hear, possible to install UNIX OSes on existing FAT32 partitions, but as a matter of personal opinion I believe it's useful to strictly stick to a "default" environment when learning a new OS -- you can always move on to more non-default, advanced features later.
You should thus end up with the following:
- your 10GB Win98 partition
- your 10GB XP partition
- the aforesaid 10GB FAT32 "common storage" partition.
- a 10 GB partition with some UNIX OS installed on
From the Linux camp comes the LILO boot manager (boot loader) that you can install, allowing you to easily select any of your OSes at startup.
I would not do away with any of my current OSes until you're fully at home in and happy with your UNIX OS.