Trust people who live here to guide you in the right directions. Steffi, and myself know the score, and places to see, and places to avoid. Steffi's right, Lands End, and Newquay are both places that are over rated, "tacky" and comercialised. Another place that isn't up my street is St Austell, it's got a huge ugly man made beach, and a town resembling a building site, But it is central for all area's of Cornwall, and it's got a brand new travel lodge which is cheap!!!!
Personally, I would start with Looe and Polperro, 2 very attractive resorts, and probably the closest resorts to you when you cross the Tamar bridge. Then on to Fowey, probably stopping off at my gorgeous village (Lerryn,) on the way, and following the road through to the car ferry to take you across to Fowey. From Fowey, I would then try and get the passenger ferry that takes you to Mevagissey for a day trip, and also across the Fowey river to Polruan, another pretty village worthy of a visit.
As most people have stated, St Ives is nice, but again, very "touristy" so a bit over rated. Try and get to "Doc Martin's" village, Port Issac, and also King Arthurs Tintagel. To be honest, a week just isn't enough to see all the lovely places Cornwall has to offer, but I will put a few links on for you to have a look at. Enjoy your stay.
http://www.themagicofcornwall.com/pages/photogallery/secornwall/looe/looe_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/secornwall/polperro/polperro_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/secornwall/talland/talland_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/secornwall/lerryn/lerryn_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/midcornwall/readymoney/readymoneycove_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/midcornwall/mevagissey/mevagissey_pics.htm
http://www.cornwalls.co.uk/Port-Isaac/
http://www.themagicofcornwall.com/pages/photogallery/ncornwall/tintagel/tintagel_pics.htm
http://www.bbc.co.uk/cornwall/photos/st_ives/1.shtml
http://www.themagicofcornwall.com/pages/photogallery/ncornwall/daymerbay/daymerbay_pics.htm
http://www.themagicofcornwall.com/pages/photogallery/ncornwall/rock/rock_pics.htm
http://www.polruan.org.uk/
Just a few pictures for you to browse through, and make some choices.
I also look after a gorgeous property in Polruan. It's near to the water, has gorgeous views, and is a good central base for travelling around the area, and it's tastefully decorated, and very clean.
http://www.english-country-cottages.co.uk/uce/ecc?view=details&action=readDetails&cottageId=405941&holidayPark=N&startdate=25/05/2008&duration=7&sleeps=2&propertyTypeId=&complexId=