Thanks, but MLLE takes ages to load a tileset... And I get a lot of errors when I try to click on the tiles. Too bad, because the tileset list is so much friendlier than in JCS.

And the first link you gave me doesn't give me idea how to do that in Windows 7. I know how to associate a file with a program. Whenever I click on J2L file it opens in JCS. But I have no idea how to make additional things described there. I tried but I don't have any of the mentioned options.