I keep my Linux and Windows on different drives. It's a personal preference, but one that I find useful for my purposes. With a 180+G drive, you can easily install numerous Linux distributions to play with.
I would initially partition that drive to have about 14 or so partitions. That would give you two partitions for each distro you want to try (for a total of 6) and a partition for /swap and one for /common. This last being a storage or archive partition that you can access from any of your Linux installations.
Initially, you would probably be only installing one Linux, possibly Ubuntu or PCLos, I would assume. If that's the case, you would mount your /(root) on one of your first partitions and /home on the next. You would also be able to access your /swap partition and common partition from this installation.
Later on, when you've become relatively comfortable with the Linux that you initially installed, you'll probably be wanting to try a couple more you run across. With those already made partitions, you'll be all set.
Here's how I would set up the partitions:
1 --> Primary --> 2Gig --> /swap
2 --> Primary --> 28Gig --> /common to all storage
3 --> Primary --> 150Gig
4 --> Extended --> 10Gig --> /root for Linux
5 --> Extended --> 15Gig --> /home for Linux
6 --> Extended --> 10Gig --> /root for Linux
7 --> Extended --> 15Gig --> /home for Linux
8 --> Extended --> 10Gig --> /root for Linux
9 --> Extended --> 15Gig --> /home for Linux
10 --> Extended --> 10Gig --> /root for Linux
11 --> Extended --> 15Gig --> /home for Linux
12 --> Extended --> 10Gig --> /root for Linux
13 --> Extended --> 15Gig --> /home for Linux
14 --> Extended --> 10Gig --> /root for Linux
15 --> Extended --> 15Gig --> /home for Linux
Disconnect your Windows hard drive completely before partitioning and installing your Linux drive. Once you have the Linux drive partitioned, install your first distro. Allow the installation to write its GRUB or LILO bootloader to the MBR (master boot record) of the Linux drive.
Set your BIOS to boot the Linux drive first. You can add a Windows entry for the Linux bootloader once you reconnect your Windows drive. This way you can easily boot either your Windows or your Linux installations at startup. Later when you install other Linux distributions, do NOT allow them to install their bootloaders. Just manually edit the original one in your first installed Linux OS to add the new installation entries.
This is how I've done it for a couple years on my systems. I currently run seven distributions of Linux and Win XP on my system. Others here may have suggestions for you that might be easier for you.
However, you choose to do it... just DO IT! You won't regret it. I went to Linux 100% almost two years ago. I only have the Windows on my system for playing games. Otherwise, I wouldn't have it at all. I can do everything I ever did in Windows with Linux, usually faster and more efficiently... and DEFINITELY MORE securely.
Have FUN while you're learning it. That's half the battle.
Luck!
~Eric