Sorry, didn't know your circumstances
Heiko Webers' (Hesky-Data Software) PAD
http://www.hds-pad.com/ is the best writing tool I've found. Good support for projects (chapters), search&replace and lots of other goodies. Not expensive. No spell-checker though. Due for an update that Heiko tells me that should come out "real soon now".
Jan Goyvaerts' EditPad Pro
http://www.editpadpro.com/ is also good with lots of bells & whistles though fractionally less easy to use and more expensive. Has a spell-checker and regular updates.
These are the two best "straight writing" apps I've found. Good luck with your endeavours!