If you want something comparable with powerpoint you need to install OpenOffice (or I think Koffice), especially if you need to be able to open powerpoint files. OpenOffice is bigger than Puppy is - I recommend install it as an .sfs addon, not as a .pet, unless you have a "full" install of Puppy. Koffice is quite a bit smaller I think, but again I'd recommend a SFS file. OpenOffice is slow and ram hungry, and I suspect your computer won't handle it very well. I think Koffice should be a bit better, but not great.
I don't know what Puppy version you have, but recent versions of AbiWord (Puppy's word processor) have a presentation plugin, which provides a full-screen presentation mode for presenting using a word processing document. It is quite limited, but probably adequate for most purposes.
Alternatively you could create a PDF - then you could use it with the full screen mode of any PDF viewer.
According to the release notes Puppy 4.3 includes Fullerscreen, an addon for Firefox/SeaMonkey for creating presentations... although they are in html.
There is also Apres, which used to be included in Puppy http://www.murga-linux.com/puppy/viewtopic.php?p=66515&search_id=628421193#66515 (I think you need to install gtk12 and lib12 from petget to use it), and of course various other methods of doing slides with image files.
There are also some obscure things like xsw and magicpoint, which you probably aren't ready for http://murga-linux.com/puppy/viewtopic.php?search_id=248921172&t=40914
Probably the best alternative if Openoffice is too heavy and Abiword too basic is Impress, which used to be in petget - I guess you can probably install it by selecting the Puppy 2.x repository in petget. If it doesn't automatically install tcl/tk you'll have to install them too.