Hi, and welcome to the forum,
You will need to restore your Windows bootloader before you can boot Windows.
You can use a bootable floppy, with the command:
If you use the Windows installation CD, then its fixmbr
Definitely back up anything before doing anything else, if you haven't already. Then it would be a good idea to defragment.
You'll need to do some partitioning. It's not difficult, the hardest part is deciding what you want. You can have four primary partitions, of which one only may be an extended partition. This extended partition may be divided into a number of Logical partitions. Windows can only be installed on a Primary partition. Linux is perfectly happy on a Logical partition.
At present you have a Primary partition (sda1), formatted NTFS, wih Windows, and an Extended partition (sda2), which is entirely filled by a Logical partition (sda5) formatted NTFS and labelled "Data". At the least, you'll need to shrink sda5 and add some logical partitions (sda6, sda7, sd8, . . .) for linux. If you want to access some of your data from both Windows and Linux, then I suggest you format a Primary partition FAT32, because I don't think Linux can write to an NTFS partition. I would suggest the following:
sda1 primary, formatted NTFS, with Windows, as at present. You *may* be able to reduce its size.
sda2 Primary, formatted FAT32. It wants to be about 25% bigger than the amount you will need a year or two hence
sda3 Extended, containing:
sda5 Logical, formatted ext3 with linux (root) 10G should do, if you keep your stuff on:
sda6 Logical, formatted ext3 Linux. Data partition . Size: Big enough to hold your stuff + 20%.
sda7 Logical, formatted swap. If you have 1G or more of RAM, 1G should be enough here.
sda8 Logical, ext3. 10G Use it for another Linux
sda9 - sdax
As above. You can either put another OS on them, use them for data, or get rid of them later.
sda4 Not used
Most people advise having a separate /home partition. The ext3 Data partition takes its place.
It's a good idea not to have your partitions too big. Linux does a file system check every so often. You can wait for a 10G partition, but for 200G you might as well go and mow the lawn or whatever. (On the other hand, you don't have to defragment with linux).
Having a second (or twenty second) Linux is good for a number of reasons. You can use it to get into your main system when you screw it up (we all do). You can try other distros out, and above all, it will help you learn - you can afford to try things out.
Use your Windows disc to resize your Windows partition. Then boot the Linux install disc, choose manual partitioning (don't be put off by the "expert" tag), and create and format your other partitions. Install the Linux bootloader (Grub) to the MBR. The new Grub should automatically give you a choice of booting to Windows or Linux.