How soon do you want the camera? The D100 won't be released until June/July and you'll likely have to wait beyond that date since companies are taking pre-orders already.
The D1x is likely to be about twice the price of the D100. For the price difference you could buy yourself some additional lenses / Compact Flash memory cards / a good colour printer / etc.
The D1x is built to the same sort of standards as the F5, and also performs in the same kind of way (very fast autofocus and so forth): do you particularly want any of the facilities it offers, or would the extra size and weight be a nuisance to you?
On a seperate note, the D1x "Pro Kit" (as it's called here in the UK) is a good buy: you get a battery, charger, Nikon Capture 2 and some other bits that are worth significantly more than the price difference over the body only.