I suppose you could blow up a 1 megapixel image to the size of Kansas, but it won't be giclee quality. The company I use for giclees recommends that images be 300 dpi for optimal results. Though acceptable results can happen at lower resolutions, you lose quality at lower resolutions.
What this translates to in my experiences is that a 10 megapixel camera (for example, my XTi) can give 300 dpi for an 8x10; anything larger means loss of fidelity.
That's why I scan anything I plan to giclee. My scanner does 300 dpi (actually 600 dpi and better scanners do better than that), and I save $100 everytime I scan it in instead of having them do it.
With giclee, you want the absolute best possible results you can manage to produce. The goal is a print that you can't tell apart from the original and that lasts indefinitely. Though perfection seems impossible, and longevity is questionable, it still merits the effort.
My 2 cents