So to clarify a little bit further on what Big_Dogs was saying:
Potential in BB is handled as a certain cap range. So starter would be 16-18, star 18-20, allstar 20-22, PAS 22-24, etc. An individual player will have a specific cap number somewhere within this range. So for example, all MVP potential players will have a cap somewhere between 26-28, but a given MVP player could be hard capped at 26.01 or at 27.99, there's no way to tell. That's the random element in potential.
The cap is calculated according to the players' skills based on the player's position. So for a PG, HA/PA have a high cap cost, OD/DR have a moderately high cap cost, and JS/JR affect it very moderately. Inside skills have no effect on salary and a minimal effect on cost. It costs more to get higher and higher pops (e.g. it will have a higher cap cost for a PG to go from 19-20 PA than for a PG to go from 5-6 PA). For a SG, JS/JR/OD affect the cap, but PA is free, which is why you'll hear people talking about wanting high PA on their SGs. SFs are highly affected by JS/REB and moderately by OD/ID, PFs are affected by JS+inside skills, and C are affected by IS/ID/REB/SB. You can find tools to calculate the exact affects of each pops on the cap on the forums here, don't have supporter so I can't find them. USA managers can use bb-usa.net to find this information.
This is also the idea behind primary and secondary skills, and why secondary skills are so coveted. Primary skills are anything that affect the cap (which also affects salary), while secondary skills are the ones that don't affect the cap (and thus not salary either). Hope all of this information I just vomited out makes sense, and is helpful. Anyone feel free to correct me if I'm wrong about something.