Hi Bobby, and welcome to the forum.
First I want to thank vidoman for his kind words, I don't get that too often

(just browse my post on this board and you will know why

, I dislike people that want to be given everything without doing anything themselves

)
I started using PI with version 8 SE, I think. I got that with some computer magazine for free. Didn't really know what to do with it but bought the upgrade to PI XL. Shortly after, my PC died on me. It didn't really die but I killed it because it was playing up

. When re-installing everything, I couldn't find my copy of the first PI program and, hence, could not install PI XL because it was an upgrade and the installer asked me for the setup.exe of the qualifying program, PI 8, which I didn't have.
To cut a long story short, I went and bought the full version PI 10 because I had started to do things with my photos. Somehow, when hunting for tutorials for PI, I came across the PIRC board
http://www.pircnet.com/ and realized there was something like a free beginners workshop for PI. I took that and never looked back.
Now back to your questions. I'm not sure where you are located and which exact version of PI 8 you are using. If you are in the USA, chances are you have the NOVA marketed version of PI. If that's the case, I'm afraid you would have to uninstall the old version, if you are thinking of getting a new one, because NOVA only allow one version to be installed at any given time. If you were to get a full version Ulead PI 12, either ESD (download) or a boxed version, you can install that alongside your old version. You just can't update from NOVA to ULEAD PI. You can buy ULEAD PI on the internet here
http://www.ulead.com/store/pi/runme.htm and, if your version is the Ulead one, not the NOVA release, you can simply buy the cheaper upgrade version. The upgrade is identical to the full version but has a loyalty discount built in. You will need the serial number of PI 8 though to install the upgrade. Having PI 8 still installed, it should be found by the installer and the installation will finish with no questions asked.
You can also get the trial version and do not need to uninstall PI 8 to use that. It will stop working after 30 days though. Also, you will not get all the extra content and EasyPalette items with the trial.
Since it has been a while since you installed PI, I wonder of your PC is up to the new version PI 12? What are your system spec's? Please note the minum requirement for PI 12:
* Intel Pentium III compatible or above
* Microsoft Windows® 2000 Service Pack 4, Windows® XP Service Pack 2 Home Edition / Professional, Windows®XP Media Center Edition, Windows® XP Professional x64 Edition
* CD-ROM Drive
* 256 MB RAM
* 750 MB available hard drive space for program and content files
* True Color or Hi-Color display adapter with 1024x768 resolutions or higher
It doesn't run on anything less than WIN2000 SP 4 and requires a lot of RAM (I use 2 GB) and is rather set on a high resolution display.
I would advice against it if your computer is not better than the minimum requirement in regards to RAM and hard disk space.