The N900 still cannot enter the Ovi Store because Nokia has not completed testing to make the terminal compatible with the shop. If you try to Ovi Store, clicking the icon of N900, appears the notice of Coming soon!.
But the community Maemo has already found a way to enter and download applications. Although it is not highly recommended, from The Nokia Blog have followed the instructions in this thread of the Maemo’s forums and have been successful.
If you can’t expect to Nokia has prepared the Ovi Store for your Nokia N900, you can try entering yourself and see what gives you for your new terminal.
I have to say I haven’t any good experience of the OVI stuff, music store requires you to use microsoft stuff if you want to use it a bit faster and it seems to be problems to login to your account (my girlfriend can only require new password, but not login to her account, so she can’t download the 10 free songs she got with her N86).
The store seems to only offer premium SMS payment in Scandinavia, which don’t work well with Asian phone subscription and I rather pay with CC than on a phone bill.
I have to say, I don’t look forward for this microsoft centered OVI store which is extremely slow (even compared with the solution I worked with for a former employer of mine, which used quite a lot of old and sloppy code).