is it possible to recalculate only a cell or a range in VBA

There is a calculate method you can call on ranges:

Range("A1").Calculate

Try it out by putting =Now() in A1 and running Calculate and watch it update the seconds :) You can for a recalc of all the cells in a sheet by using:

Sheets(1).Calculate

See also: Microsoft MSDN, Excel Recalculation, 16 July 2012.