I think that partition magic might work, but I have not used it. You can also use "qtparted" or "gtparted". The first is available on the Knoppix Live CD.
The first thing to do is to backup your system, then defrag the disk.
If you just want to try things out for a bit, I would suggest using the Live CD (Knoppix, Ubuntu, DSL OS, etc.). You can try some things without making any changes to your disk.
Also, I would suggest not having a single partition even if you use just Windoze.
There might be some versions of Linux which can be installed on the existing partition, but most need to have their own partitions.
My personal suggestion is to have a Windoze partition of around 10Gb or so, a boot partition of 100Mb, a root partition of around 6Gb and then the rest in reasonable sized partitions. Unless you need a really large partition, you have more options available if you have smaller partitions so that you can change things in the future.