Cracking salted md5

Hello there,

I'm trying to crack a salted md5 password, but I haven't been able to figure it out from the wiki or the command-line help. I wanted to ask you for some help on how to get started. Btw, I'm using cudaHashcat v1.20

So, basically I have an MD5 hash which has been generated using a salt. I know the salt, not the password (obviously).

The MD5 generation process is like this
$salt = "username:magic word:";
md5($salt.$password);

At this point I don't know how to give the salt to Hashcat so that it takes it into account.

This is the command I'm using at the moment:
cudaHashcat64.exe -t 20 -a 3 --outfile=testresult.txt --outfile-format=3 myhash.hash ?a

The hashfile only contains the MD5, where do I put the salt string?
Also, is it a problem that the salt itself includes strings like ":" ?

My command line is probably way off apart from the attack and hashing type. Would you please advise me?

Thanks!