Performance management is based on past performance. For example looking at sales made by a salesperson last week. Where as talent management is assigning the right job to the righ man. This is done by forecasting the ability of a person to perform in future for specific tasks.... by analysis of personal traits and by finding about personal goals of a person etc. Performance management is a relatively easy task as compared to talent management. Talent management also involves training and or developing. Identification of fast learners and people capable of performing better under new/unseen conditions.
The relationship between 2 is that Talent management comes 1st and it effects the performance. So if the results of performance management show that performance is low. The area of investigation should include talent management. may be wrong people have been picked to do the job. May be they need more training and development to perform well etc.