ATtiny and ATMega1284 cores - installing for 1.5.4

I have a reasonable selection of AVR controllers (ATtiny84, ATtiny85, ATtiny4313, '1284) as well as the usual '168 and '328 ones, as well as official Uno, Due and Mega boards.

Following posts in the developers mailing list, I would like to use 1.5.4 as the IDE (on a Win7 x86 machine).
On my (now dead) XP box, I had 84/85 and 1284 cores in 1.0.

What I'd like to do is have cores for all of the above available in 1.5.4, and I'm probably not the only one.

Can anyone provide an easy-to-follow guide as to (a) where to get them, and (b) how to integrate them into the 1.5.4 IDE?

Google/Bing/search engine of choice will solve (a), although there appear to be multiple versions for tiny support, while maniacbug seems to have produced the de facto code for the 1284 chip.

All of the things I've read relate either to 022 (or earlier) and 1.0 versions of the IDE, and I can't seem to consistently get it working.

Note that I'm not talking about actually "programming" the controllers. I have built carrier boards (generally with ZIF sockets) which allow me to connect an AVR ISP mkII and handle that (and of course, on the 1284 use a bootloader).

It's the actual integration of the "board" I am having trouble with.

Thanks in advance

Steve S