The wallmart website looks to be down for maintenance at the moment, ill take a look when its back online.
Something to consider is if you’re buying a pre built pc wait until the 1st of July and you will get a free upgrade to Windows 7 when it’s released. Some websites name June 26th as the date, some name it as July 1st.
Free Upgrade to Windows 7 Program for Windows Vista PC from July 1 My Digital Life
Lifehacker - Best Buy's Upgrade Pricing for Windows 7: Free, $50, $100 Depending on Your Situation - windows 7