Please help a newbie. Need to replace equipment.

I bought a house with an 18000 gallon pool (according to some blueprints I found, but when I do the generic calculation in seems it's closer to 20,000g)
it is in-ground plaster. ( appr. 13' w, 32' l, 4 ft - 8 ft deep )
I have a sand filter, if I remember correctly it is appr. 60-80 gallons, I have never been completely happy with it even though I replaced the sand over 1 year ago.
I have what looks to be a vintage 1-1/2 hp sta-rite pump with 1-1/2 s40 pvc pipeline. From what I have read on the sister "poolsolutions" site, it is obviously oversized.
My motor burned 2 days ago due to some flooding in the area (not serious thankfully) and with the pump being full of leaks, oversized, and the motor burning, it is finally time to upgrade. (please keep in mind my equipment is at least 10, maybe 20 years old, guesstimate)
From what I have read in this awesome website, the more expensive DE filter is probably in my near future. I called a couple of local places, and depending on who you talk to, I need a 36 or 48 filter.
As far as the pump goes, everybody is telling me to buy a minimum of 1 hp or more (no surprise), I would like to stick to my guns and maybe buy a 3/4 hp.
One place told me if I buy a 3/4 hp it would have to be "high head".
Does anybody have any suggestions? Thanks for your help.

First, your pool is probably no more than 18000 gallons using the standard formula: 13*32*6 (ave depth) * 7.48 = 18670. But usually, steps and curves at the bottom reduce it further so it could very well be 18,000.

Second, this should probably be posted in the pool equipment & operations section: http://www.poolforum.com/pf2/forumdisplay.php?f=144

For 18000 gallons, a 3/4 HP motor is more than enough. However, if you have a spa, water features or a vacuum, it may not be enough so a 2 speed would be better.