I have only recently started to scratch the surface. But from what I have seen so far, the easiest and and most straightforward path into development is to use psl1ight
http://psl1ght.net/wiki/Main_Page it is a homebrew project and supported by the community. Another bonus is that I think it falls out of the legal grey area(or wavers close) so online resources and contributors won't be ousted.
Secondly, and somewhat more risky is to use the SDK. It looks as though there are some serious with getting this to run as files are signed to cooperate specifically with debug/tool PS3 console versions. A number of stages must be manually implemented to sign the final project file for deployment on a homebrew PS3 dev OS. As of the legal issues surrounding this, almost no support exists, no advise or discussion and links to software and resources are long dead.
I've worked on the PS3 SDK legally through my university and it is a blast, I have yet to test psl1ight completely, so I have no stake on it yet.
Primarily, you want to get a NAND/NOR flash chip, depending on PS3 version and flash the hardware to enable to downgrade the firmware (version 3.5) to install a custom OS or whatever you fancy. This process is only compatible with the older phat models.
How comfortable are we here with discussing grey material? I plan to write a tutorial for getting started on PS3 dev (both methods) so I wonder if this is acceptable to post in the future.