I’ve been able in the past to download some old public domain cartoons off of usenet. because of the nature of usenet (I guess) they’ve had to be broken up into a number of parts each which has to be played separately. So, a two part question …
1 : Is there a way or some software I can use to splice two mpeg files together seamlessly to make one big file?
2 : Will the same process work on mp3 files?
2 ideas
#1 use adobe premier 5> which is designed for that sort of thing but this baby costs about $700
#2 edit a playlist for the mpegs in windows media player (WIN98SE , 2K and winME only) or use someother suitable
program with a playlist facility winamp comes to mind with plug in for MPEG video support somewhere i recall
I’m not sure if this is the same thing that your thinking of or not… but, if I am downloading multipart MPGs throught the usenet, this is what I do.
I highlite them all (CTRL and click them). Usually the filenames are like “CARTOON PART 1 of 5”… I select all of them. Then, I right click on them and select COMBINE+DECODE and it combines them all together to make 1 file that you can then save.
Give it a shot.
there are two (freeware, iirc) app.'s that’ll do it, if you play a little with the extentions… they are hjsplit and Mastersplitter.
I’m sure, if you look around, you should find either easily enough, either through a search engine, or at Tucows.
Basically, the files have to all be identical, as in, moviename.mpg.001, moviename.mpg.002, moviename.mpg.003, etc…
Mastersplitter sometimes uses a .000 file, and if it’s not there, it’ll ask for it, but it’s not required.
Glenoled
Yep … I found Mastersplitter and it did the job. (Not a bad price too at $10.00.)
Thanks!
All your porn questions answered here, at the SDMB! 
What are you using as a usenet reader?
I use Hogwasher on the Macintosh, which automatically tells you whether or not all the sections are available; displays files, not individual posting lines containing parts of a file; and has extremely customizable filters for helping to weed out the spam. When you download a split file, it downloads all the parts, joins them together, and associates them with one of your programs based on the file extension. Drag and drop to the desktop or select Save from the file menu.
I’ll bet you can find something equivalent for Windows at TUCOWS if you look.
When fishing around for Binaries on Usenet, I found that Agent does the job best. It will combine multipart messages for you, and also join multipart-multipart messages. For example, full-lenght movies are often posted as many multipart messages. HTH.
I think the shoe is on the other foot here, for once. Boy, I can’t count all the threads that got stomped by moderators just for discussing techniques that COULD be used with Usenet binaries and such. Are your cartoons (ahem) really public domain? AFAIK, they’d have to be films released before 1926 and the creator died before 1951. Something like that. 
But seriously, Quicktime Pro does a wonderful job of copy and paste assembly on MPEG files. You can even trim parts and do simple edits and save the new file, no recompression or re-rendering required.
But if your files are like filename.mpg.000, filename.mpg.001 etc, the PeeCee people usually intend these to be rejoined with MasterSplitter. Never use it myself. On MacOS X, I just rejoin with
cat filename.mpg.* > filename.mpg