If you are confused with CrowSan's post, it is a typo, it should be "Ha-tagged-X and Myc-tagged-Y".
If the interacting partner for your protein of interest is unknown, you can still identify it. Most people run the co-IP on SDS-PAGE, locate and excise the unknown band after silver staining, and do trypsin digest for mass spectrometry analysis. I cannot give you the details, as I do not work on this stuff. You can send your sample to the core facility of your university for custom service.
Not affiliated with any company. Mention of a specifc product does not imply my endorsement of the product. No conflict of interest or guarantee to work on the advice given. Do as I say, not as I do. Not liable to the loss of your valuable samples.