Free software

[Fragony]

But DreamSpark doesnt give you Windows OS or MS Office for free so I doubt whatever the OP is using is legal.

Open-office works really well http://www.openoffice.org/

[Husar]

http://msdn.microsoft.com/en-us/academic/default

For Office there are discounts depending on the country you live in, I got mine for 60€, and it's the Professional version(has Outlook and Access etc. unlike the Home and Student thing) but students only.

Through MSDNAA I got Windows for free but with 7 they only allowed one installation so I bought a heavily discounted upgrade for my notebook as well.

The problem with OpenOffice is that it is fine for a lot of people but once you want to do more sophisticated stuff you can get problems and the presentations will often get borked up when you load them in PowerPoint apparently.

[Fragony]

Not if you save your files as a ppt, it uses a different format by default, never had any problems beyond the suckiness of powerpoint in general.

[Husar]

Not if you save your files as a ppt, it uses a different format by default, never had any problems beyond the suckiness of powerpoint in general.

No. If you save them in .odp or what it's called then PowerPoint cannot open them at all. If you save them in .ppt then you can still get problems with text, pictures, animations etc., for some reason the two seem to interprete the .ppt files a bit differently. It doesn't always happen but I wouldn't take the chances either.
I don't use PowerPoint a lot except for uni presentations and that's where I heard about such incompatibilities as well.

[Fragony]

Never happened to me, always used mac version though. I found open-office to be better than the official one, especially MS Word is packed with little and big annoyances. Better to use notepad and copy paste to word.

[Strike For The South]

Freshman year of college I went out and BOUGHT a 300$ copy of windows only to find out later it was free on the schools website

I quickly lost faith in God and humanity after that