Ok, here's an easy way to do it. Select all the files you want to RAR. Right Click the selected files, Select "Add to Archive", which should be added after you install WinRAR. A new window pops up. Enter the filename you want to save the rar as, and then note the box in the lower-left hand corner of this window. You'll see "Split to Volumes...". This is where you enter the volume size and it will break up the archive in the size you specify (in bytes). So if you enter 15000000, it will break the archive into 15 meg chunks (I personally use 15 megs, its fairly common, 20 megs is also, I really don't reccoment the 1.45 disk size megs in today's day of broadband, but its up to you
Click OK and it will archive and save to the same dir as the files you were archiving. The files will be filename.partxx.rar, xx being 01, 02, etc.
Have fun with it!.
Oh, and I mean right click just in the folder, not in the WinRar program itself. Also, this should probably be moved to the Technical Forum, so Mods of this forum, when you have a chance