Having more than one OS on multiple drives or partitions is not only not a problem, it's actually a good idea. This way, should anything ever happen that prevents you from booting from your main drive, you can boot from your second drive. If the drive is new/blank, you may also want to consider partitioning the drive using Disk Utilities. This gives you multiple 'drives' within the drive, any of which can have OSX installed on it. If you format a partition with MS-DOS, you can use it for Windows.
Partitioning basically turns one large drive into several smaller ones. Each partition looks and behaves just like a normal drive, and you can transfer files between them. One advantage of partitioning is that should your drive suffer a failure, it should only affect the partition where the problem occurred. For example, lets say you divide a drive into 4 partitions. (you can customize the size of each partition, or use the default, which divides them equally) You have installed OSX onto partitions 1 and 2, leaving 3 and 4 for files and/or backup. You normally boot from partition 1, when it unexpectedly fails and you can no longer boot from it. Depending on the type of failure, it is very likely that partitions 2, 3 and 4 are fine, letting you boot from partition 2. Now, You can run Disk Utilities, or any commercial hard drive utility you may have. Had the drive not been partitioned, the entire drive would have failed. FYI, your Mac will automatically boot from partition 2 if it is unable to boot from partition 1.
You can still lose an entire drive that is partitioned, but unless the drive suffers from certain hardware failures, this is unlikely. It is always a good idea to backup and identify the problem quickly during any kind of hard drive failure, even if it only affects one partition.
Another use for partitions is for backups. Let's use the same 4 partitions as above. If you boot from partition 1, you can have Time Machine back your files onto partition 3, providing extra protection should partition 1 (or 3) fail. You could also use partition 4 to backup 2 in the same manner.
To be even safer, you can use Time Machine to backup onto another actual hard drive, which can also be partitioned. There are countless ways to set this up, but let's say you have 2 hard drives, each having 2 partitions. You can have OSX on partition 1 of each drive, then have Time Machine use partition 2 of the other drive to backup in a criss-cross manner. This way, your files are protected should either drive suffer from a partial or total failure.
One last benefit to multiple boot drives/partitions is that once in a while, an update can be buggy or even render an application temporarily useless. One example is how the latest Quicktime update affected several games under OSX.4. The games that were affected could not be used at all, and you had to either wait for a patch from the game's developers, or use an earlier version of Quicktime. Quicktime cannot be uninstalled or reverted to an earlier version, so this was a major pain for several people. However, so long as the OS on partition 2 had not been updated yet, partition 2 could be still be used to run these games. This is just one example, but most any app could be affected this way by an update, especially third party apps. It has also been known to happen when upgrading to the next full version of OSX. This is also where it is GOOD that the OSs run independently, answering your other question.
It is important to know that partitioning a drive WILL ERASE IT, so either start with a new drive, or backup/clone the drive before partitioning it. I know it's a lot to digest, and I hope haven't confused you, (and please forgive if you knew any of this already) but you can also search "partitions" in the Finder's help menu.
Will this cause any conflicts at all? Will I be able to boot into either one? Will the two exchange files, or use the same settings and configurations, etc.? Or will they leave each other alone and run independently?
