This is a difficult (but possible) collection level. It took a while for me to beat it...
Download it here: BonetowersGishColLvl.zip
For me all towers at the top collapse within 20 seconds (before you can reach them).
Alright, I made a few modifications and re-uploaded the map. It's likely that I had uploaded an old version of the map before. Hopefully this will fix it...
That's weird...I'll look at it and see if I can fix it later today.
I got to the end. 
29.5x (without the highscore file or replay I can't find the exact time)
It may be pushing floats through the limits. In the Windows version more calculations are done in double because visual C doesn't cast when it should.
I made a little movie of what happens when you just sit still. Blame the video capture software for the slowness and choppy sound.
On my machine it plays very slowly. I only have a 650mhz athlon though (I like CL games because their requirements are usually less the commercial ones)
I've not managed to get past about half way - the long tower you have to climb to get to the ceiling, always collapses before I get to the top.
Anyway, as I said, the exceptionally low framerate makes it no fun to play at all.
Mark
The physics are quite a bit over the top for your specs.