You have to make connection to server using ODBC or OLEDB to do this. Please take a look at the call escape sequence topic in Books Online. The url is mk:@MSITStore:D:\Program%20Files\Microsoft%20SQL%20Server%20Books%20Online\1033\odbcsql.chm::/od_6_035_5dnp.htm. You may have to change the path depending on your installation. You can also find samples in the SQL Server CD.
Calling normal stored procedures from Extended Procedures
Calling normal stored procedures from Extended Procedures
BrianZim