So, here's the thing: You can get pretty close at home, but unless you're at expert-stylist level (and hey, you may be), your hair isn't going to look expertly styled.
Go to a pro -- a beautiful blow-out it doesn't have to cost an arm. There are moderately priced experts out there. And then, make that pro job last. Rather than washing it, "wash" it with dry shampoo, only at the roots (and not where your part your hair). At night, wrap it gently in a silk hair wrap (or scarf). Your hair will look perfect for days rather than hours.
And through it all, keep in mind: Kate, poor thing, is expected to have perfect hair. We lucky commoners can get by looking pretty darn good on a daily basis, hit the salon for a special treat and bam -- knock 'em dead and go to sleep smiling (in a silk hair wrap).
For more information on hair care and other princess-type things, look over the links on the next page.