Stefan,

One way to do it is to use two separate queries, one for YTD and one for
MTD, the join the two on salesman in a third one and base your report on
that third one.
The first two queries must be Totals queries, with fields for Salesman,
Sales and calculated field(s) on Date.
Use Total function Group By on salesman, Sum on sales and Where on the
calculated field(s) on date.
YTD query requires one calc.field, e.g. MyYear: Year([datefield]), with
criterion Year(Date())
MTD query requires two calc. fields, one same as above and another for the
month, e.g. MyMonth: Month([datefield]), with criterion Month(Date()).
Them make a third query incorporating the previous two, join on salesman and
get the fields for salesman, YTD (SunOfSales from YTD) and MTD (SunOfSales
from MTD) in the grid. This is all you need for your report.

HTH,
Nikos