LabVIEW should function properly with your GPIB card using VISA. However, you may need to use the card's manufacturer's version of VISA - which manufacturer made your card? If it's National Instruments, then you can use the 488 support that comes with LabVIEW and NI-VISA.
With regards to the RS232 portion of your question, that depends on whether the instrument has a RS232 port and supports serial commands and data (see your instrument programming manual). In addition, a device such as the GPIB-232CT can be used to go from RS-232 to GPIB, but is probably not necessary since you already have a GPIB card.
