Stuart, make sure have the System requirements
Here are the recommended memory (MB or GB of RAM) and processor speed (GHz) requirements for using Audacity with different versions of Vista:
Vista Home Basic
2 GB / 1 GHz
512 MB / 1 GHz
All other Vista versions
4 GB / 2 GHz
1 GB / 1 GHz
Note that the minimum system requirements as defined above (i.e. those that allow the operating system to run, ignoring what is required to run applications) are much greater than for Windows XP. If your computer does not significantly exceed these minimum requirements then you may have problems doing more intensive tasks in Audacity such as recording for long periods or editing a large number of long tracks, or may need to close other programs and processes before you can do so. Please be aware that the cheapest "deals" for new Vista machines may well only include the Vista Home Basic Edition and system specifications little in excess of the Vista minimum requirements.
Other things being equal, 64-bit
versions of Vista will require more RAM than 32-bit versions. While some users report Audacity runs fine on 64-bit Vista with 2 GB RAM, this depends on the number of tracks being worked with and the number of other programs and services running on the computer. Memory is now very inexpensive. The general recommendation for 64-bit Vista is to install a minimum of 4 GB RAM - and for very best performance, install the maximum RAM that your motherboard supports.
If you meet the min system requirements. Uninstall your sound card drives and try the beta version for Windows Vista.