Getting Married In Spain - Obtaining Residence Card Question

I am an American, and have lived in Spain with my girlfriend for 8 years, with trips back to the States every 4 or 5 months for a few weeks. Obviously my status in Spain is illegal. I have been registered on the Padron for 2 years, and before that another 3 years. I have had a rental contract for 6 years, have a bank account, and Movistar contract also. My fiancée is Russian, but has had a Tarjeta de Residencia for 5 years, and has now obtained her first 5 year Residence card. We want to get married, so I do not have to worry about overstaying my 90 tourist visa restrictions. We love each other, but the process of me being in the USA for 6 months or so to obtain a retirement Visa is too long for us to be apart.

Is it possible for us to be married in Spain while I am there, and after that for me to receive a residence card making me legal??

What documents must I/we have to do this and how long might it take. Iappreciate ANY insight because we are a little desperate and just want to be together.

Thanks