Is there a way within Oscommerce to upload products in bulk via an excel spreadsheet?

By defaul that option is not supported by oscommerce
but you can make custom script for this,

You can go to www.scriptlance.com, and post a project to someone make this script...

they have many choices on their forum

Hello cmtusa,

Yes - you need to install the ezpopulate contribution. This will take data from an excel spreadsheet and move it to a temp forward, then populate the database.

Additionally, you can place the image file names in the appropriate column and simply ftp the images into your /images directory - this will automatically attach your images to the products you imported.