Try:

DECLARE cspInit IN csp32.dll LONG nComPort

One warning:
In VB this declaration (function with no specified return type) means that function returns result of Variant data type. Since DECLARE statement in VFP does not support this data type (See "DECLARE - DLL Command" topic in VFP7 help), I give you statemet without return type specified. If this doesn't work (or return data is useful for you), you can try declare function with some return type (LONG, for instance):

DECLARE LONG cspInit IN csp32.dll LONG nComPort