I'm trying to analyze a list in Excel but I need some help.

I have list of values in column A (let's say, e.g., the numbers 1
through 100).

I want to compare a single value against the list by creating a box
where the user types a value and Excel checks that value against the
list. If the value is not on the list, a msg box displays such; if
the value is on the list, a msg box displays such and adds the value
to the next column.

E.g.:
A user opens Excel...
In column A are the values 1 to 100.
Somewhere to the right of column A is a txt box or other control where
the user can type a value.
If, the user types '231' a msg box displays 'value not on the list.'
If, the user types '44' a msg box displays 'value is on the list,'
then inserts the number 44 in cell B1.

Any thoughts? Thanks for any help.

alex