If you are using FC switches (e.g. Brocade 300's or so), you can very easily do this.
If you are using 2 dual port HBAs and are currently using 1 port per HBA to the existing SAN, you can indeed use the other port on each HBA (via the same switches) to the other SAN. I'd highly recommend to properly zone the setup where any given HBA port can only talk to 1 of the SANs (cleaner).
An example of the zoning:
Zone 1: Server 1 HBA 1 Port 1 -> Array 1 Controller 0 FC port 0
Zone 2: Server 1 HBA 1 Port 1 -> Array 1 Controller 1 FC port 0
Zone 3: Server 1 HBA 2 Port 1 -> Array 1 Controller 0 FC port 1
Zone 4: Server 1 HBA 2 Port 1 -> Array 1 Controller 1 FC port 1
Zone 5: Server 1 HBA 1 Port 2 -> Array 2 Controller 0 FC port 0
Zone 6: Server 1 HBA 1 Port 2 -> Array 2 Controller 1 FC port 0
Zone 7: Server 1 HBA 2 Port 2 -> Array 2 Controller 0 FC port 1
Zone 8: Server 1 HBA 2 Port 2 -> Array 2 Controller 1 FC port 1
This may seem like a lot of work initially, but with the help of the aliases in Brocade's zoning this is pretty easy to set up if you know what you are doing.
Dell does offer services to do this zoning for you I believe and these aren't too badly priced last I saw/heard.
