Would this code cause memoryleaks?
you select the pen in, but don't select out before delete.

SelectObject(memDC, hp353535);
// snip
DeleteObject(hp353535)


should be:

hOldPen = SelectObject(memDC, hp353535);
// snip
SelectObject( memDC, hOldPen );
DeleteObject(hp353535)

SelectObject(memDC, hBMP); should really be hOldBMP = SelectObject(memDC, hBMP);


For some other comments:


I recommend that you split the WM_PAINT (and all other messages) processing into its own function. It'll be easier to read/debug.
Are rMainClntNoBorder (and rTile, rClnt) globals, or declared and initialised before the code supplied?
Only declare one variable per line. It's easier to read and find where it's declared rather than searching. It also avoids an issue with pointers that you may come across.
Use proper names for the brushes if you can - hbDarkOrange (or even hbCurrentActiveTile) means more than hb984921.
Unless you have hundreds of colours, it may be better to create them at the start of the program and delete them at the end, and store their values in a struct in the 'user-area' of the window structure - You may want to avoid creating and deleting them continually.
If you don't do the above, keep the creation and deletion as close together as possible.

hbDarkGrey = CreateSolidBrush(RGB(33, 33, 33));
FillRect(memDC, &amp;rMainClntNoBorder, hbDarkGrey);
DeleteObject( hbDarkGrey );

Similarly, your switch statement could be simplified. Rather than creating three brushes and using one, just pick the one you want.

setTileRect(); // implies that rTile is a global??
switch(tiles)
{
    case 1:
        tile_colour = RGB( 73, 73, 73 );
        break;
    case 2:
        tile_colour = RGB( 152, 73, 33 );
        break;
    case 7: // allow fallthrough
    default: // you need a default!!
        tile_colour = RGB( 0, 0, 0 );
        break;
}
hbTile = CreateSolidBrush( tile_colour );
FillRect( memDC, &amp;rTile, hbTile );
DeleteObject( hbTile );

Instead of 1 and 2 etc in the case statement, create some meaningful constants for them with enum.