First of all, welcome to the LUG, and yes, seeing as you wish to use Logic 8, this is the correct forum. It is indeed possible to transfer projects from Logic 5.x to Logic 8. If they are Logic "only" projects, i.e. they do not contain any instances of 3rd party software such as vst's, the transition should be fairly straightforward, with the caveat that Logic 8 may have some trouble with long names (more than 32 characters) of audio files - you may need to help it find some audio files manually. Make sure you know which folders they are located in.
If you were using VSTs in your old projects (perhaps you used the windows version of Logic 5?) then it gets a little more complicated. If you wish to use these plugins with your projects in Logic 8. first of all you will need current AU Versions to be installed. Secondly, the settings of the VST Plugins will not survive the transition from Windows VST to Mac AU. Before I go into more detail, it would make sense for you to give us some more information.
I was indeed using a PC version, and some of the projects i started do use VSTs, although not all of them and it may be possible to replicate them i would have thought. Is there anything else you need to know from me?
Heads up as well - I'm not sure, but version 8 may well not open version 5 songs (although I certainly could be wrong - your initial information may have covered this). Possible you might have to open and save these in a newer version to get L8 to recognize them.
I transferred many projects from PC Logic 5.5.1 to MAC Logic 8 - flawless! 3rd party plug-ins obviously didn't port over, same with a few redundant Logic plug-ins (eg 3.0 reverb) but the icons, colour scheme, track names, relative volumes, pans, edits, tempo changes etc made it over easilly. You will need to delete your Bus's and use Aux's instead to allow L8 to look after your mixer, perform a little tidying up work and maybe import a cleaner 'template' from a dedicated L8 song of yours, but otherwise it's a no-brainer! Just make sure you use a copy of the L5 project, not the original just in case.