Look [link=http://www.rcuniverse.com/forum/Virtual_Pro_Bro/m_1482178/tm.htm]here[/link].
There I've posted a simple Fun-Fly model for FMS (actually I moded it from an existing one). You will need to use your transmitter, because with the keyboard it's just not possible and also not realistic.
But beware, with Windows XP the paralel port interface doesn't work, so you may need to use the serial one, or you can get the paralel interface, and partition your HD to have both the Win 98 and WinXP. But before partitioning, make a backup of all your data, since it's highly probable to lose it in the process, happned to me when I partitioned mine.

Hope it helps,