Hi,
i know a little bit of Unix, but not a whole lot.
I have a PC with W2K running on it.

I want to install redhat Linux 7.3 as new OS in dual boot.

do I need to install a boot manager like system commander or does the linux install detects other OS'es and create a dual boot 4 me (like dual boot W98 / W2K for instance)

Also, r there other things I have to watch out for?

Check out linuxdocs for tons of info on installing dual boot with lilo, grub, or native windows bootloader...
Here's one that may be useful:
http://www.linuxdocs.org/HOWTOs/mini/Linux+WinNT.html

I know that there are others too, such as using the different bootloaders, and other setup stuff.

The only thing I recommend, is do not mount your windows drives read-write when you are booted into Linux. This isn't something you have to worry about by default, but if you go out of your way to access your win2k partitions writable from Linux, the filesystem will get broken. Unless you fix it a certain way after each time you write to an NTFS partition, you will be unable to boot 2k.

But you shouldn't really have too much to worry about - it's hard to break the fs (you have to recompile the kernel just to allow yourself write access). The other thing to be careful about is repartitioning. You can accidentally (very possibly, unless you have the right tools - read the howto for info) wipe out your partition table, rendering the data you already have on your drive unreadable. Take a backup if possible.

I've done dual-boot before with no problems whatsoever, though... you just have to make sure you know what you're doing

linux comes with a boot manger, LILO. you can install over fat32, but not NTFS.

Unless you plan on crippling your performance, I wouldn't install on fat32 either. That's not very useful for many people. Repartition / resize, and install on ext3 / reiserfs filesystems.

Redhat now offers both lilo and grub, although I think grub is default now. I finally gave up on lilo, and gave grub a shot - it's not too bad... I just have to figure out how to use it

rdhat 7.1came with LILO by def. and I don't think i saw grub. oh well, earlier version (7.1) and yeah, over fat32 isslow as heck- that's why i only use a 250MB partition for windows and the rest for Linux! (1GB drive1, 800MB drive0, 100MHz, 32MB ram)