it's not that you need to declare a whole bunch of 'HEAP' type tables, but as the MYD files are accessed, they are actually ( where available ) sucked into RAM and cached automagically...
linux does this for you...
now, what i do is at startup, do a command like "cp /path/to/all/my/*.MYD /dev/null"
that gets the ball rolling immediately...
with 32gigs of ram, i'm off and running then with the OS handling all the writebacks on change
if you every look at your server ram usage, after it has been running for a long time, you will notice that regardless of how much RAM you have, there seems to be a very high percentage 'in use'... i reality, the OS is just hedging it's bets and using RAM wherever possible...
right now, for example my 32 GIG ram server is 'using' 29Gigs, but not really, if you get my drift...
normally i would NEVER get a 32 gig ram server, but i got 'lucky' in that there was a bad MOBO that caused a lot of pain and i was repaid with 4 sticks of 8Gigs to 'make me go away and stop complaining'
bottom line, regardless of myisam or innodb.... RAM RAM RAM!!
get all you can and more.. it's cheap.... and it beats banging the HDD
