Altering a large table to INNODB
Hmmm... puzzling that a 4GB operation of any sort should take a day.

I recently answered a question on binary compatibility between versions here. The relevant IMHO bit from that post is quoted below (from the documentation):

 - Export and Import (mysqldump)

You can use mysqldump to dump your tables on one machine and then
import the dump files on the other machine. Using this method, 
It does not matter whether the formats differ or if your tables 
contain floating-point data.


I would always advise that users, if at all possible, use plain text solutions (scripts and the like). This is in the vein of Unix philosophy and therefore, what I would strongly advise you to do is to: 


Stop replication
Backup your single table as per the community wiki here, i.e. using mysqldump.
Manually edit the mysqldump script to change the engine from MyIsam to InnoDB. Check out Rolando's more detailled answer above mine - although he did say it was "short and sweet" :-). Use this command sed -i 's/ENGINE=MyISAM/ENGINE=InnoDB/g' your_schema_dump.sql as per here.
Reload table as per wiki.
Recommence replication (same reference as for stopping).


Et voilà! 

I don't know your disk setup, but I'm willing to bet that it will take nothing like 24 hours (minutes maybe? :-) ).