Up until now, menu systems for MOSS had to be built if you created new site collections that resided below the “parent” site (Parent in a URL-hierarchal sense). The team at RDA have released a few projects, but by far and away the best one from them (IMHO) is the Global Navigation solution in CodePlex.
Basically, you can nominate a web site or set of web sites you want to have the navigation based on, then using a separate administration page, Staple it to whichever web sites you want. I hope to try it out on one of our lab servers soon, and if it works as described I’ll just start rolling this out as a matter of course for all of the clients I create intranet sites for, where you will often have separate site collections with separate navigation in the same URL hierarchy.
You can get the code and binaries for it here – there’s also a blog entry with screen shots here – I just wish they’d explain what they mean by the phrase “associating a Data Source with all sites” – Is the web site the data source? A Database table?