chris,
dont rely too much on the sat nav, they are still 2 year behind, had a load of hassle with tomtom who insist they are up to date, yet if you use google maps(which they use by the way) you will see which roads are not yet updated,
best bit of advice is take your time at the roundabouts and you should fathom them out, here are some more murcia co ordinates should you need them,
Alicante Airport - N 38.28728 W 0.55829
Ikea Murcia - N 38.02627 W 1.14610
Condado - N 37.72241 W 1.36404
La Torre - N 37.82669 W 1.00078
Cartagena Harbour - N 37.59769 W 0.98382
San Javier Airport - N 37.77546 W 0.81854
Peurto Mazarron - N 37.56460 W 1.25859
cheers ant