Describing what im after is not going to be easy, please bear with me on
these!!

Firstly I was wondering if its possible for a cell to auto populate with a
formula if other cells have data added to them. For example, say I type Bob
into C3 and Smith into D3, without having to do anything manually my self can
I get excel (via VB or whatever) to automatically to populate E3 with a
concatenate formula showing C3 & D3 together? Could I then do this for an
entire column so when extra lines are inserted, the same thing occurs??
(Fingers crossed this makes sense)

Secondly, I would like to know if its possible to create a sum total based
on categories selected in other cells.
For example, I have 3 categories: First, Additional & replacement. First
funnily enough is always the first number to be stated in the list, then
there can be any number of Additionals on top of that. Replacements however
override everything that has gone before it and effectively reset the sum to
what the Replacement is worth, Additionals can also be added on top of these
Replacements. Can I get a sum to intelligently see what categories are added
to a list as they are added and calculate the equivalent totals?

Eg

First 1
Add 1

Sum Shows 2

First 1
Add 1
Replacement 24

Sum shows 24


If anyone can understand what im trying to create and help me out that would
be fantastic.

Many thanks in advance,

Rikki