Continuous line graph using multiple rows of data?

Really hoping you can help with this! I just cannot find a way round this:

Data for three customers is shown in multiple rows, but each customer in the graph needs to be shown as a continuous line, is there any way I can do this?
(I can't put the data into one continuous row)

Example data:
Week 1 Week 2 Week 3 Week 4
Customer 1 100 100 100 100
Customer 2 90 90 90 90
Customer 3 80 80 80 80

Week 5 Week 6 etc
Customer 1 100 100
Customer 2 90 90
Customer 3 80 80

Any help you can give gratefully received!

Thanks for this example, I'm sorry but could you provide a little more detail? Although I have used a named range it displays them as 6 different series, rather than 3 continuous lines? When I tried it on the example you kindly did the graph seems to do the same thing (there was no detail in the graph when I opened it), and displays two series rather than one continuous line? I fear I'm misunderstanding what to do?

2007 version

Thank you, I think skipping the commas was causing me the problem. I have managed to make the line continuous, but the resulting graph is very strange in terms of values - although when I add data labels the values shown are correct, they have 'stacked on top of each other' on the graph rather than overlapping (which they would with the true data) - so are shown at incorrect values.
Would it be easier if I sent you what I have been able to produce?
Your help with this is truly appreciated so thank you!

Thanks, example attached of what I have managed to produce, as you will see I can't get the lines of the graph to line up correctly with axis.
I'm sure it's something simple!

Unfortunately, it moved the starting point of each line onto the axis, but didn't locate the lines correctly?

Thank you! How embarrassing, what a silly mistake! All your help has been appreciated.

First: Thanks, this definitely helps with the basics.

In my scenario, I have about 50 rows. These rows change every week. Is there an easy way to do this?

I have started with: Sheet1!$A$5:$G$5,Sheet1!$A$10:$G$10,Sheet1!$A$15:$G$15,Sheet1!$A$20:$G$20

As you can see, this would be a huge string. How can it be condensed?

Thank You

Thank You, FDibbins - You are correct. I apologize, and will start a new thread.