First Off, get the Trial Version Of Macromedia Flash MX 2004 (or buy the full version) from:
http://www.macromedia.com/software/flash/

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First Open it and Choose Flash Document.

Adjust The Canvas To The Size Of Your Sig.

Than press control+R and import your sig.

Than press F8 and press Button and click OK.

Than double click on the sig.

Now press control+r again and import the song.

Now click on the little dot (.) below the Up section.

Than you will see a new menu opend,In the sound option where it says
None click on it and choose your song.

Next press on Sync and select Stop.

Now next to the up section you will see something that's called Over Right click on the white
screen below it and choose Insert Keyframe.

Than choose your song again,and in Sync choose Start.

Now click ctrl+enter to check if your sig is working.

Now click on Scene 1.

Now click File->Publish Setting.

Now you can see a folder icon,click on it and choose the place where do you want to
save it.

Now you can see something called Formats next to it Flash click on it.

Now click Override Sound Settings (Its in the bottom of the page).

Than click Publish,than click OK than check if your sig is done.

[Just A Side Note:]

Thanks. :)

You wouldn't by any chance know why my Flash claims it can't read some of the songs I tell it to, even though it could before?

Is the file .wav , .mp3 or .wav?

mp3, and like I said, some files the program has read before and doesn't now.

sorry to bump this but anyone know where i can upload the files to put them in my sig and if i need the flash and the html uploaded

You Need To Download Flash MX 2004 And You Don't Need To Upload The Songs. You Just Need To Have Them On Your PC.

cool tut and all but i can't get mine to play the whole song...

o no i knew i didnt need to uplaod the song or anything i fixed everything but i cant get it to show in my sig do u know the code to get that to work and i upload the flash file someone to get it to work right cause i have it uploaded on putfile.com right now just cant get it to show in my sig

You need the .swf file from Flash.

no i got the file uploaded ijust dont know the code to put in my sig thats the only problem

Look In The First Post. Where It Says CODE. Copy That And Fill Out The Height And Width And URLs.

And You Need To Upload It On PHOTOBUCKET And You Need The URL For The .swf FLASH FILE.

hmm it wont let me upload it to photobucket for some reason lol it hates me

Filesize might be too big. You can compress it but I forget how.