Depends on what you mean by joint problems really..? Degenerative changes (OA or DJD) in the knee-, hip-, sacroiliac- or lumbar joints perhaps?
Good non-stressing exercise would be swimming, pilates, yoga, redcord training, subtle horseback riding, crosscountry skiing, stability training, mat exercises, aqua-training and cycling; all of which place almost no stress on the joints in question.
Stability training for stomach and back would also be heavilly recommended as a supplement to this type of exercise i.e. training on a exercise ball, bird-dog exercise and 'the bridge'.
All the best,
Alex (D C. Mchiro).