Maxamis, your client has really chosen good option. SharePoint 2010 along with Access 2010, is really really powerful. I am using it for about two years and I know its potential. Reason are many like : Data is stored centrally on SharePoint lists (tables) which acts as back end and Front end is Access 2010. I can list down so many benefits, of using SharePoint...(But right now, I'll not go into details of it )
However, to answer your question, Pl. follow following steps:Internet Explorer
Local Site (Not internet)
Go to Internet Options->Security
Click on Local Intranet then click on sites and advanced.
Add your SharePoint site to this list then click add then close and OK.
On the same window, click Custom Level and scroll down to the bottom of that list where it says "User Authentication"
Change this to Automatic log on with current user name and password.
External SharePoint Site (Internet Site, not recommended)
Same steps as above, but click on Trusted Sites to add your SharePoint site
Then click on internet to adjust permission levels
You can also check following site :
http://technet.microsoft.com/en-us/l...ffice.13).aspx