With Premiere Pro, slideshows are handled by Encore. It may be possible to import your existing slideshows into Encore CS5.
You have used Send to PrE for your PSE SlideShow, correct?
Once in PrE, choose Break Apart, to separate the SlideShow into the constituent parts. Now, do a Save_As and alter the Project's name a bit. This will create a new PREL (Project file), with the unique name.
In PrPro CS5, first try to Open that PREL. There will be a dialog screen telling you that it was created in PrE, but PrPro should be able to Convert that PREL to a PrPro PRPROJ file. If not, then create a New Project in CS5 and Import the PREL into that.
If neither works (I can only talk about PrE 4 PREL's into PrPro 2.0, which works well in almost all cases), then back in PrE, Export/Share to an AV file. Personally, I would use the Lagarith Lossless CODEC, but you will need to download and install that, rebooting afterwards, to use it. Import that AV file into CS5.
I do not think CS5 imports Elements projects.
It says so in the manual but when you look at the import window supported files: no PREL.
You could well be correct, and I can only base my experiences on earlier PrE and PrPro. I do not believe that CS2 mentioned PREL files either, and I had to do Show All Files, but then the PREL Opened just fine. When I tested, I tried to come up with some PrE Projects that would cause issues, and found that Instant Movie and Themes threw errors, as did some of the NewBlueFX Transitions and Effects, that were not in CS2. Same thing happens with PRPROJ files from earlier versions, where 3rd party and discontinued Effects and Transitions obviously cannot Import properly.
I'd still try this, and monitor the results. I would be interested to see what CS5 says. Also, as stated above, from the Open dialog screen, only PRPROJ files will likely show, so one needs to use the little drop-down for Show All Files.
[Edit] Just went back to PrPro CS2 and Opened a PrE 4 PREL. Actually, the PREL's showed fine in the PrPro Open Project dialog. If they do not in CS5, that might lend credence to Ann's comments. Still, I'd try with Show All Files.
Message was edited by: Bill Hunt - Added [Edit]
My PPro CS5 offers .ppj,, .prel and .prproj as file types when opening a project, so it looks hopeful. But since I don't have Elements, I can't check it actually works.