i can mini mash about eight pounds of grain in a 20 quart ss kettle. i have a spigot on it now, and am working on a better filter element than stuffing some scouring pads (the brass ones maybe, not with soap...

) in the end of the spigot...

this lets me drain the wort out and not mess up the grain bed too much. before i was dumping the whole mash through a large collander into my brewpot, then pouring the hot water over, with ok results, but i noticed a better flavor and more punch with the method i describe below.
i add one quart of water per pound of grain to my 5 gallon kettle, bring the water up to about 175 F, take the kettle off the heat, then add the grain and give it a whirl... it should stabalize at about 155 or so. put the lid on it, then it goes into the oven at lowest setting simply to maintain the 155 degees for an hour, oh yea, start yer oven ahead of time if you want to do it this way. i start to boil a bunch of water, usually three or four gallons at this time.
the water i've heated in the other kettle to 170 or sometimes higher as the heat bleeds off when i take it from the stove and loses a bit whilst sparging, i slowly siphon over the mash pot... i poked some holes in the end of a tube and just let it lay across the grain bed and drain the sweet wort out into my beer boiling kettle.
then i add the dme while the kettle is still off the heat and bring it back up to a boil....
enjoy! the enhancement in taste going from a simple grain steep with six lbs of malt extract to a mini mash with half the extract will blow you away. and when you look at the bill, like i do now, you'll say... gah!!!! no more malt extract!!!! i am anxiously awaiting my spring time transition to all grain!
have fun, let us know how it goes.