Can I sort by definition? And auto-fill lists?

Newly registered user struggling to find the right terms to search on what I want to find out so while I'm searching, I'll ask as well. Hope thats OK.

I update a daily incident report that is sorted by priority of the request as well as the date/time. In the past, I've recorded and run macro's to add a number to a priority so that it can sort numerically. Lately I've been tasked with building similar functionality into more reports. I am wondering whether I can tell Excel what order to sort items into (ie "Sort by HIGH, then MEDIUM-HIGH, then MEDIUM, then LOW)?

With regards to auto-fill lists (for want of the proper name), I report on multiple IT systems that fall into six "system" categories. Is there a way I can set up the "System" column to automatically update the correct data once the IT service is entered, rather than manually look up systems category then click the relevant system in the drop down box?

I'm pretty confident all this is possible and probably very easy once I know how. I just don't know what the Excel terms for doing that are, which makes finding out tricky.

1st, as you have a macro already, I think you can change the number defined for the prorieties' to control the order to sort
2nd, Vookup is a good choice for you to find out the correct date, see the excel help for details