This is what I have a problem with.

If they enter A in C4, I want them to tab to the following cells for data
entry: e4-i4, then m4-o4, then s4-u4, then y4-aa4, then ae4-ah4, then
al4-an4, then ar4-av4, then az4-bc4, then bg4-bj4, then mn4-bq4, then bu4-by4
then cc4-cg4, then ck4-co4, then cs4-cx4, then db4-dd4, then dh4-dj4, then
dn4-dp4, then st4-dv4, then dz4-eb4.

But, if they enter P or S in C4, I need them to only
enter data in the following cells: d4, l4, r4, x4, ad4, ak4, aq4, ay4, bf4,
bm4, bt4, cb4, cj4, cr4, da4, dg4, dm4, ds4 and dy4.

At this point when they hit the Tab Key, I want them to the beginning in the
next row. I know this may be impossible, if so, please just say so. I have
spent several days trying to figure out if this can be done, my boss wants it
to be possible.