Drop down lists - multiple values

Hi everyone

I'd like to include a drop down list in an excel column hosted on Sharepoint, but where multiple values can be selected in the same cell (and where one selection doesn't over-write the previous selection).  I created a macro to enable this but when uploaded to Sharepoint it wouldn't work.  Google tells me that Sharepoint won't accept macros.  Anyone know of a simple way round this?  Thanks, Adrian