Your field appears to comprise three sub-fields - a two character code (JV in your example) a date (30aprl2011 in your example) and an autonumber field - so ou could use access autonumber field, together with two other fields (the code and the date) to build the field you require - use a 'view' if you need to to present that field.
If you really want the numbering to restart at 1 for every date or code change then you will have to program it yourself - by finding the maximum value of the field for the existing code and date, then adding one two the 'counter' portion at the end
you could use something like
select max(field) from table where field like 'JV-30Aprl2011-*'
I don't recall the Access syntax off the top of my head - but you should get the idea.
I was going to send a link to an Access program that did almost exactly what you wanted - but you asked for no links, so there you go.