Field Programmable Gate Arrays (FPGAs) are able to provide a high computational parallelism that can be exploited to achieve high performance improvements in intensive data processing problems. In this paper our efforts were directed towards developing a PC cluster based on nodes that use FPGAs as co-processors. The target application is a floating-point large dense matrix multiplication. Experimental results for just one node of the cluster, consisting of a Xilinx Virtex 5 VLX50T with a PCI interface, showed performance improvements compared with the Intel Core2 Quad at 2.66 GHz, achieving a speed-up of 1.19 times. Other analyses in terms of frequency variation and power dissipation have been made by considering different matrix sizes running in one node of the cluster. Recently, the platform has been updated for a powerful Gidel plaftorm, the PROCe III 260E. This new platform consists of 1 FPGA Stratix III per board. In this board, it is possible to allocate up to 40 MACs per FPGA, reaching an overall speed-up of approximately 11.2 per node of the cluster when compared with the same general-purpose processor. A full example is presented in this paper.