It seems useful to blog an edited and tidied up response I gave.
About the transferFirstly, it is difficult. The more accounts you have, the harder it is, and the more inter-currency transfers you have, the harder still.
On my FAQ site, the relevant article I used was the QIF route (http://moneymvps.org/faq/article/28.aspx), which is the mechanism I used for the basic account moves (using QIF export/import), but when doing the transfer, there is also the need to factor in the creation of scheduled bills, recreating the budget (if you use it) and planning data.
If you have a Pocket PC which you synchronize, then note there is no PPC program
for Money 2007 (at least from Microsoft).
How long it tookI had quite a lot of historical accounts which only linked between themselves, so in a sense they were easy as I did them before doing the main accounts that I use today. Similarly with investments. No idea how long that took, as in a sense, that was some of my dry-run data.
I didn't copy any planning data and I regenerated my bills/deposits from the existing data (I manage my accounts so that I have as few as these as possible, so there were no complex loans for example). Inventory I didn't care about.
Finally I took the plunge and did the main accounts (I had done dry runs before this). I then sorted out the tranfers which used different currencies, and it probably took a few hours in total
To help matters, it was done using Microsoft Virtual PC, so I could have both the US and UK versions open at the same time.
This is not something I would necessarily recommend, and you need to be committed to do it, otherwise you may waste a good few hours of your life. If you want to do it, then you may like to check out the trial version of US money first (http://moneymvps.org/downloads/trials/default.aspx and use that to perform dry runs and tests.