My travel partner and I are planning for a trip to Spain the last week of March and first week of April. Is that time of year good for San Sebastian? Thanks.

if you are looking for beach weather : NO

It won´t be cold, but not too warm either. It rains almost every week, so be prepared.

Rain is why the area is referred to as "Green Spain".

If you are travelling next year then the first week of April is Easter, that means high season prices and hotels etc fuller than normal, you never know when you will get sun in northern Spain.

Short answer: No!
Easter is Apr. 4, 2010, so you're looking at 'Peak Season' rates everywhere in Spain during that time period (Semana Santa).
San Sebastian is likely to be cold and rainy.

Many Spaniards desert larger cities like Madrid and head for southern shores for Semana Santa. Swim against that Tide! Head for Madrid and enjoy a week there (including Toledo and Segovia).

Thanks for the information, everyone. Yes, I am expecting higher prices depending on where we head.