Are you splitting them for the sole purpose of posting them?
Because if you have larger files that you are wanting to split into 100mb chunks for posting, you
can use winrar for that
without having to split the files beforehand.
I thought from your original post that you were starting out with small files that you wanted to join together.
So say you have a 300mb file you want to post, right click on the file (assuming you have a PC) and choose "Add to archive". When the winrar window pops up, in the lower lefthand corner there is a pull-down menu that says "split to volumes, bytes", one of the preset pulldown options is "98,078k-Zip100" which works just fine for Rapidshare etc. (or you can enter an amout in the line if you so choose). Hit "ok" and you will wind up with 3 files that looke like "Filename.part1.rar, Filename.part2.rar, Filename.part3.rar" in 98 meg chunks. Unlike the scenario earlier in the post, this time when the person downloads all 3 parts and extracts them they
will have one big file, because that's what you started out with.
Hopefully that's what you were looking for originally.
edit: To see what I'm talking about, check out
My Video Post. The last post is a perfect example of the output.