Opinions on equipment+acoustics on large rooms

Hello gurus.

I would like some advice in selecting equipment for playing
music (mainly international folk) to an audience of 100+ people in a large room (60L x 30W x 18H), puplic school type
with cement block walls and no carpeting.
How many watts RMS am I going to need?
What kind of speakers? Any ideas to improve acoustics in such a room?
Would hunging curtains on the wall behind the speakers help?

Thank you in advance.
unless they're all gonna' dance, you need to figure out how to plug in 100+ pairs of head phones. alternatively, you can issue everyone in the audiance an acoustic panel and have em' hold them up, arms outstretched, whilst standing around the optimal perimeter (establihed by trial-and-error); anybody remaining after the panels are handed out should be able to hear ok. and dance, if the spirit moves em'. fact is, you probably ain't gonna' get this space to sound very good unless you hire a pro sound group to set it up. -cfb
I hope others jump in because I will not claim the crown as the guru you might be seeking (now, Sean and others are another story). You have some real advantages in your room dimensions. The height to width ratio is pretty good and the length of the room allows for a 20Hz wave to have lots of breathing room. The people themselves will provide for some damping, but wall treatment wouldn't hurt -- center rear absorption material and some side wall mats or rugs would be good.

Watts are deceiving -- I've had a 600 watt RMS amp that strained at higher volumes and one that I simply could not turn up to nearly that level without hurting myself. Look for amps with big power supplies (even down to a couple of hundred watts if you're not looking for super high volumes). Look for speakers that extend down to the bass depths that the room allows and that are as efficient as the amp requires (the beefier the amp, the less efficient the speakers you need to use). You may, depending on the speakers and amps available, need to consider help from a subwoofer. A softer top end might be a good thing since the room sounds like it might be bright.

It sounds like you have a choice in speakers and amps. If so, go big -- it's a lot easier on the ears to turn it down that clip it up. You might want to do an Audiogon Discussion Forum search on "Acoustics" to find many better ideas. What are your choices? Are you looking at professional or home gear? Good luck. I hope this helped.
If U can't go cornfed's, pro, way, check available -- top-quality -- horsepower first. Try active speakers or active bi(multi?)-amping. My guess is you'll need an easy +110db delivering capacity in the full room so, check out the speakers' handling limits!! So, try to get the loudest possible uncompressed, clear sound during the sound checks.

IMO, whatever you do the 1st row will go deaf & the last may need a hearing aid...

As the empty room WILL echo Oz's suggested damping is very important.
In lieu of a tall rack, spread out the equip on smaller supports.

Use of a spectrum analyser would help -- even a rat-shack mike+tone signals, etc. -- for placement.

Make sure the music is "public school" certified!:)

Most of all, good luck!!
I guess my question is, how high fidelity are you going for . If you are playing live chamber music it is goign to be different than your local rock band.
The solution could easily run into the many thousands of dollars or be much less depending on your goals.