...basically, when acrobat is installed it creates a printer, a pdf writer...
...if you have it, you will find it in your print options as an available printer...
...if not listed then you need another way, cutepdf writer is free, and acts just like you were printing to a desktop printer, only that you are really printing to a digital pdf file instead...
...from powerpoint, file > page setup, check settings are as required, choose the pdf printer driver, print to your desktop space > open photoshop > file > open > locate pdf > turn anti-aliasing on in the dialog > set resolution to either 300 or 600, which ever is most suitable, 600 would be preferable if text is involved for high end output...
Andrew