You can use the Find command: Edit /Find; in the Find window you will have the possibility of choosing Search in "Comments".
With vba, you have to specify "xlComments" in the LookIn option; for example:
Cells.Find(What:="WORD", After:=ActiveCell, LookIn:=xlComments, LookAt:= _
xlPart, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase:=False _
, SearchFormat:=False).Activate
Does this help? Bye.