Dealing with custom menus first, I'm not exactly sure what you mean, but did you add custom menus in Excel 2003 using similar steps to these?
If so, then in Excel 2010, use it's Help option to search for Custom Menu bars, and see if that helps. If not, perhaps this will;
Now your first question about Macros. See if this helps; http://www.dummies.com/how-to/content/how-to-set-the-macro-security-level-in-excel-2010.html
May I ask? Have you tested all these workbooks in the newer Excel yet? If not may I suggest you make copies of the workbooks first, (using Explorer but not Excel itself), and test the copies. Why? I can't really say because I don't have Excel 2010 myself, but it is different and the VBA may be different. Best to see if the macros transfer over using copies of files first, in case any are stripped out or corrupted. It's only a precaution.
I am being upgraded to the new(er) version of Excel, and there are two things I can not imediately see how to do.
The first involves macros, I use a lot of spreadsheets containing macros, and sometimes I want them to run, sometimes I don't.
In excel 2003, this is really simple, I just use Tools / Macro Security / High ( or Low) as needed.
How can I achieve this in the 2010 version?
Secondly, I have a number of macro's I use all the time, saved in my Personal.xls file.
In Excel 2003, I added a custom menu, and added custom menu items to the drop down list, and assigned macros to these.
How can I replicate this in Excel 2010 ?