Testing a model that has been trained after PCA

Hi,

I have a question regarding dimensionality reduction using PCA.

If I have a train set (train.arff, 10 attributes) I perform a PCA and I save my data with respect to the new transformed variables (say I choose the two first attribues, combination of the original ones, that collect most of the variance), and call this transformed trainset "trainset-afterPCA.arff".
Now I train a model using this file (which only has 2 attributes), and save it.

If now I have a new dataset, constructed with the original 10 attributes, and I want to use the model I built before to classify this new data, how do I have to proceed?
1. If I just try to test on this new dataset, train and test are'nt compatible, right?
2. If I ran PCA on the test set, the resulting new attributes won't be the same as the ones obtained in the training set.

What should I do?
:(

Thank you a lot for this useful forum