Create a custom unit at initialization

Im trying to create a custom unit at the map initialization, but when using the function:

call CreateUnit(whichPlayer, 'hpea', peonX + 0.00 * unitSpacing, peonY + 1.00 * unitSpacing, bj_UNIT_FACING)

i dont know what to do, cause i dont want to create the deafault pesant "hpea", but my own custom one. How do i do that and where do i find all those "aliases" for the units?

Tnx for the help, hope i was clear

Control-D in the object editor to get raw data, and look at the name for the custom unit, it'll be a 4-character ASCII code like 'h000' or something, put that in (if in ' ' it will convert it from characters to a number using ASCII).

tnx :)