The file size is the best. Below is a list of all versions of outlook express (that i have) and has all the file sizes and the file to look for. ITs a little rough but im sure will do the job.

Code:
 

45716,"Microsoft Outlook Express 5 build 5.00.0913.0800","msimn.exe","",0,0,"","","","(|FileSize=39312,39312)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45717,"Microsoft Outlook Express 5 build 5.00.0913.2200","msimn.exe","",0,0,"","","","(|FileSize=33388,33388)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45718,"Microsoft Outlook Express 5 build 5.00.0913.2204","msimn.exe","",0,0,"","","","(|FileSize=48494,48494)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45719,"Microsoft Outlook Express 5 build 5.00.0913.2206","msimn.exe","",0,0,"","","","(|FileSize=39000,39000)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45720,"Microsoft Outlook Express 5 build 5.00.0913.2207","msimn.exe","",0,0,"","","","(|FileSize=33404,33404)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45721,"Microsoft Outlook Express 5 build 5.00.1011.1301","msimn.exe","",0,0,"","","","(|FileSize=41408,41408)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45722,"Microsoft Outlook Express 5 build 5.00.2014.203","msimn.exe","",0,0,"","","","(|FileSize=42528,42528)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45723,"Microsoft Outlook Express 5 build 5.00.2014.207x","msimn.exe","",0,0,"","","","(|FileSize=45328,45328)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45724,"Microsoft Outlook Express 5 build 5.00.2014.211","msimn.exe","",0,0,"","","","(|FileSize=42256,42256)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45725,"Microsoft Outlook Express 5 build 5.00.2615.200","msimn.exe","",0,0,"","","","(|FileSize=49152,49152)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45726,"Microsoft Outlook Express 5.00","msimn.exe","",0,0,"","","","(|FileSize=39114,39114)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45727,"Microsoft Outlook Express 5.01 SP2","msimn.exe","",0,0,"","","","(|FileSize=42768,42768|FileTime=12.05,12.05|FileDate=20000721,20000721)","Microsoft Corporation","Internet and Communications Utilities","Microsoft Windows Family 9x/Me/NT/XP","()","",0,
45728,"Microsoft Outlook Express 5.0x","msimn.exe","",0,0,"","","","(|FileSize=26896,26896)","Microsoft Corporation","Internet and Communications Utilities","","()","",0,
45729,"Microsoft Outlook Express 6.0 (Beta Build 2462)","msimn.exe","",0,0,"","","","(|FileSize=41984,41984|FileTime=22.18,22.18|FileDate=20010316,20010316)","Microsoft Corporation","Internet and Communications Utilities","Microsoft Windows Family 9x/Me/NT/XP","()","",0,
45730,"Microsoft Outlook Express 6.0 (Build 2600)","msimn.exe","",0,0,"","","","(|FileSize=57344,57344|FileTime=22.32,23.32|FileDate=20010817,20010817)","Microsoft Corporation","Internet and Communications Utilities","Microsoft Windows Family 9x/Me/NT/XP","()","",0,
_________________________
If at first you don't succeed, try again. Then quit. There's no use being a damn fool about it. - W.C Fields