Merge with conditional row removal

[Thom Burnett <Thom.Burnett@cognigencorp.com>]

How do I subset a data frame so that it has no rows with a column value 
that exists in another data frame?
As an example:

fullData:
ID AGE
1    25
2    13
3    36
4    55
5    36

moreData:

ID BMI
2    23.3
4    27.4

fullMinusMore:

ID AGE
1    25
3    36
5    36

What I seem to need is a method that compares to vectors (or better data 
frames columns) and tells me if any element of A is in B.
Then I can NOT that and select the remaining rows.

Are there UNION and INTERSECTION operators in S+?