it's pretty easy to do, but might take you a few extra minutes your first try. as for frame rates, they will go down a little bit depending on your altitude and weather. my rates were at 20/sec with this screenshot and i use onboard audio/video ;)
microlight, to upgrade the terrain mesh, you have two choices. here's a qoute taken from the topic i read on the scenery board to find out how to do this:
download file: srtm_to_bgl_104.zip from avsim.
This progrma create mesh for fs2002 ans f2004
SRTM_TO_BGL automates the production of FS2002 mesh scenery from Nasa's SRTM 1 arc second (30 metre) and 3 arc second (90 metre) data. The program creates a batch file and .INF file ready for use with the SDK mesh tools. Very easy to use!!! Version 1.04 adds some new features and bug fixes. (CW)
Data :
ftp://edcsgs9.cr.usgs.gov/pub/data/srtm
basically, you need to go to that website and download the appropriate files based on lat/long and the 1 sec arc data (sounds complicated but its really not). then put them in the same folder as the program you downloaded from avsim.com (listed above). then follow the steps from the readme.txt file.
the 2nd choice is to go here:
http://www.simviation.com/fsdterrainusa.htmyou can download each area and unzip them into your addon scenery folder. i would recommend doing this first to see if you like it since it is much easier. once you do this, run fs9 and go to settings->scenery library->add area. then browse to your addon scenery folder and select the folders you unzipped (ex: los angeles). after doing this for all the new folders, you MUST exit fs9 and then run fs9 or else the scenery will not be loaded right away.
finally, it seems to me that the level of detail is better when you use the freeware program to make your own mesh files. so if you really get into it, then definitely do that instead of just downloading them. i fly KLAS->KLAX all the time and i have made accurate meshes to cover the entire trip!
ok, wow. thats the most i've typed in a week! i wouldn't have put forth that much effort if i didn't think the difference between the stock fs9 terrain and the new terrain was a big deal. but in fact, i've seen a massive difference. hope all this info helps!