I'm not an expert, but I've done it several times with few problems.
1. If you have a new disk, you can create a partition you intend to use for linux using msdos fdisk. If you need to shrink a partition non-destructively to make room for linux, you can use fips.exe.
When you run the Red Hat installation program, you can create and format your linux partition with linux fdisk or with Disk Druid. (Actually, you can even do a partitionless redhat installation with redhat 6.2.)
2. During the installation program, you can install LILO (LInux LOader), which will allow you to boot either linux or msdos [windows].
3. One thing I don't know is whether LILO will have problems with such a large disk. You can check out http://www.linux.com/howto/mini/Large-Disk-1.html. I haven't read it yet myself, since I don't have a large disk, so I'm clueless on this point.
My experience was that linux is not that hard to install. The harder part is getting proficient at using it well.