Currently there's no easy way in the API to set system currency rate. This is good to have in the API since setting the currency rate programmatically is probably what most Adempiere system owners need. It's also a step to perhaps create a central server based solution where all adempiere system's can update their currency rates automatically.
I've created and tested a new function in MConversionRate for this purpose. It uses ISO currency codes as parameters so it will be easy to call externally without having to convert to Adempiere ID:s first.
I've added static fields in MConversionType for the existing conversion types. I don't really see a situation where these ID:s would change, hence the simple hard coded values.
Please review the changes in attached patch.
Code committed 2009-05-31.
Fix: Close transaction in the end (otherwise it's a connection leak).
http://adempiere.svn.sourceforge.net/adempiere/?rev=10642&view=rev