Probably the easiest way to do this is backup your WSS3 farm and restore it to a temporary WSS3 farm (on 64-bit h/w etc.) without the content databases. Do an in-place upgrade to SP2010. The upgrade will migrate the SSPs to SSAs in the SP2010 farm. Back these up and restore to your production SP2010 farm, along with any configuration.
You can also restore your SSP database and restore that to your SP2010 farm. This requires some further configuration and Powershell work. See: http://technet.microsoft.com/en-us/library/cc263299.aspx#SSP