Good advice from [MENTION=219801]Beaulieu[/MENTION] and [MENTION=233915]LondonCanuck[/MENTION]
Terminal 2 (where the BA flight arrives) is quite small so you shouldn't have too long a wait for your luggage.
The Arlanda Express airport train offers landside free transfers between terminals but it it probably quicker to walk than potentially wait 15 minutes for a 2 minute train ride.