Is it possible to make a drop down list that branches out similar to the Windows start menu. I want to incorporate a main list of items which points to sublists of sizes for each item on an order placing form. (The sizes being the desired input).

No. You would need to use two combo boxes the first one to select the broad category the second, based on the first, would show the specific sizes related to the item selected in the first combo box. This article, written for Access2000 will work for Access97 as well, will show you how to do this...
http://support.microsoft.com/support/kb/articles/Q209/5/76.ASP?LN=EN-US&SD=gn&FR=0&qry=q209576&rnk=1&src=DHCS_MSPSS_gn_SRCH&SPR=ACC2000