There is a little GP tool that comes as part of Integration Manager. It's called table import. Basically this little guy will let you import a tab or comma delimited file into ONE table in GP. You can't combine tables, you can't link stuff, etc. This tool is a hammer, not a Swiss Army knife.
But it can be useful for tables not available in IM (like sales tax rates). The astute DB's in the audience are asking why they would use Table Import when they can just use the fabulous tools in SQL server. Well, Table Import does provide the table specifications and some basic error checking while setting up the import, to make sure that you aren't screwing up the GP tables. So if you are not familiar with the wonderfully exotic table structure or you don't have a copy of Accolade's Information Flow and Posting book handy, the basic error checking could save your behind. Alternatively, you could be arrogant and blame the application instead of your ingorance when you screw things up but I know that DB's never do that. (Sigh, there goes my DB audience.)
Table Import is available in GP via Tools->Integrate->Table Import. This tool is so straightforward that if you've ever imported anything, you'll probably get it. If you've never imported anything, pretend this post doesn't exist and call your DB for help. Yeah. The one I just drove away.