Instead of renewing your subscription for an old antivirus program you may want to consider upgrading to a current version. Most modern Antivirus and Internet Security programs can be installed on 3 computers. click here for Norton's offerings.
You can use a different AV program on your laptop if you prefer and might want to look at AVG Free version click here.
There can be problems networking Vista and XP but your best option is to try it and post back with any specific problems.