i have a ford laser rally car in australia (tx3 model which is the GT spec). the stuff spooki is talking about is called rain-X and its a spray that you polish into the windscreen. theres one for the outside that fills the gaps in the glass and makes the rain slide off, and another one for the inside that stops the glass fogging up. it works really well, i wouldnt want to enter an event without it.
the best word of advice for rallying i could give is before you enter, make sure the cars in really good shape. dont start with it already broken cause it''ll only go downhill from there. make sure your suspension is how you like it and that all the bolts are nice and tight. And make sure you get some decent oil in the gearbox- redline shockproof lightweight is fantastic (the blue one).