Flow control should be RTS/CTS a.k.a. hardware handshaking. But your cable needs the RTS/CTS lines connected for this to work.
For proper file transfer you should use a protocol with error detection/correction, for example zmodem. To use this with NComm you need
http://aminet.net/comm/term/xprzmodem.lha
On the PC I always used HyperTerm which comes with Windows XP. It still runs on Win7 although it behaves a bit weird regarding its config files.
(I only used it to transfer AExplorer anyway
)