Let DataEnvironment is dtenvTestEnv and Command is cdTestCommand. Use:
Dim prmTestParameter as Parameter

'Here you must set other parameter properties, as described bellow code!!!
prmTestParameter.Value = [Your_Value]
dtenvTestEnv.Commands("cdTestCommand").Parameters.Append prmTestParameter
dtenvTestEnv.Commands("cdTestCommand").Execute

Before you set Value, you must set following parameter properties:
-Attributes;
-Direction (input/output, as declared in stared procedure);
-Name ( = name, which expect your stored procedure);
-NumericScale (depends on declared parameter type in stored procedure);
-Precision (depends on declared parameter type in stored procedure);
-Size (depends on declared parameter type in stored procedure);
-Type ( = declared parameter type in stored procedure).

Refer MSDN topic "Parameter Object (ADO)" for futher information.