Heh - you did remember it correctly, but I'm not surprised by the confusion. Norihito is indeed Prince Takamodo's personal name - his full name wass "Takamado-no-miya Norihito shinno", with Takamodo being a historical family name he took shortly before marriage in 1986. Princess Tsuguko, whom I mentioned above as the most likely candidate to marry a Windsor, is his daughter. (Her full name is "Takamado-no-miya Tsuguko-nyoo".)
Japanese names can be tricky, especially with the Imperial family, who change family names around (not terribly rare elsewhere in Japanese society, either).
He was 7th in line. Also, he was Emperor Showa's nephew, not grandson. His father was Prince Mikasa, Showa's younger brother. (On the subject of name changes, Showa was known in childhood as Michi-no-miya Hirohito, on ascension simly as The Emperor/Tenno-samma, and postumously as Emperor Showa.)
And looking
that up brings to mind a possible problem/side-effect - Prince Mikasa's history would have some interesting effects on how this would go down in the UK. I'm sure there'd be some controversy over his involvement in China, but probably ameliorated by his indictment of Japan's conduct there.
Edit: I dug up
this montage of pics of Tsuguko - definately not the typical shy retiring type the IHA wants her to be! She's into hip-hop and had a bit of scandal about 5 years ago. Supposedly she had a blog in which she was posting about her sex life, as well as supposedly making use of Mixi, a Japanese social networking site, with some rather explicit posts.