DO these versions mean anything to me as a developer? I understand they have limitations on connections/processors/etc but none of that matters to me for a local development instance. All of the ISOs on MSDN are the same size, does it make a difference which of these I choose to download?
Developer is fine for development but can't be used in production systems for lisencing reasons. It's a lot cheaper than the others too.
The Developer edition is identical to the Enterprise edition, so you get all the feature you'll probably ever need. It's just not licensed for production use.
Standard edition (and Web edition) are somewhat limited in their functionality.
Developer edition is available at $49 in the US, so I'd definitely pick that one, if you need a dev platform!
The difference is in licensing mostly (Developer vs. Enterprise).
For development you wish to have the engine with all bells and whistles enabled, that is either Enterprise or Developer.
If you're only developing for customers then Developer will suffice. You hand-over the project to the customer and don't put it to operation yourself.
If it's your own product, then you will need un-Developer version sooner or later. By the moment of putting the software in production latest, that is.
Use the development version as it will allow you to develop with features that are available on all of the production versions. If you were to install say just the Standard version then you would be unable to develop anything that uses an Enterprise feature.
http://www.microsoft.com/Sqlserver/2005/en/us/compare-features.aspx