A BE36 pilot departed HEF on the ARSNL2 departure; but his lack of familiarity with the GPS and lack of confidence because of low recent experience caused a track deviation as ATC questioned his route after takeoff.

Narrative

From HEF Clearance Delivery I was assigned Arsenal 2 departure; MOL transition. On takeoff; began left turn to intercept CSN 056R and contacted Potomac Departure. Checked in; told to maintain 2;000 FT and was immediately asked about my routing. Having not flown the procedure; I became concerned that I had misunderstood the departure clearance and stopped my turn toward CSN. After confirming my written clearance I read it back to ATC and was told that I missed the turn to CSN and to turn immediately to heading 190. I made the turn and leveled at 2;000 FT. After a few moments I was cleared direct to MOL and to climb to 8;000 FT. Using the RNAV system; I entered MOL which gave me a course of approximately 330 degrees. As I began making the turn; I realized that this was not the correct course and by the time I realized my error; the Controller came back asking me where I was going. I responded 'direct MOL' as I was turning toward the correct course. This was my first IFR flight plan in a small aircraft in several years; having only recently returned to general aviation. I did review the appropriate procedures and was familiar with the relative geographic position of the airport; CSN; MOL and Class B airspace having flown in the area for many years. Unfortunately; I did not account for my own uncertainty when queried by ATC for my route. My relative lack of experience in the aircraft and; more significantly; with the Garmin GPS demanded more of me than expected. The result was that as I focused on flying the aircraft and attempting to derive the necessary information from the navigation system; I lost basic situational awareness allowing the Controller's question to cast doubt in my plan (which it was not intended to do) and the GPS to lead me in a direction that I knew was not correct. To prevent future occurrences; I must increase my familiarity with the aircraft and the navigation system to reduce the considerable workload of flying single pilot.