Those two setups are REALLY different. Your current gearing yields some tiny gears. Again, I would suggest running the actual numbers on Sheldon Brown's gear calculator. From there, ask yourself what gears you actually use on your current setup to see whether the Giant would work for you as a cross bike.
Yeah - WOW. Those are hugely different gear set ups.
Sarah
When it's easy, ride hard; when it's hard, ride easy.
2011 Volagi Liscio
2010 Pegoretti Love #3 "Manovelo"
2011 Mercian Vincitore Special
2003 Eddy Merckx Team SC - stolen
2001 Colnago Ovalmaster Stars and Stripes