To make it a variable, you need to declare a string, assign it and put the string variable in the place of "PR_WINTER". That is...

Dim strSpreadsheet as String

strSpreadsheet = "PR_WINTER"

DoCmd.TransferSpreadsheet acExport, 8, strSpreadsheet, "N:\ROI_08\Reports\ROILIVE" & Format(Date, "MMDDYY"), True, ""

__________________
Greg Serrano
Michigan Dept. of Environmental Quality
Air Quality Division