Hello Alex,
Good to hear about your VS observations.
The VSS spreadshseet automatically converts UT to JD, as Gary says, which is absolutely painless.
If you need to convert UT to JD (or vice versa) at any other time, there is a great Applet on the BAA Computing Section web site:
http://britastro.org/computing/applets_jd.html
This is also linked from the front page of the VSS web site.
Jeremy