Pulling data from another workbook if the data corresponds with current workbook

[Ryan1996]

So essentially i have two workbooks.

One looks something like this:
[TABLE="width: 652"]
<colgroup><col><col><col><col></colgroup><tbody>[TR]
[TD]Username[/TD]
[TD]First name[/TD]
[TD]Last name[/TD]
[TD]Ticket number[/TD]
[/TR]
[TR]
[TD]User1[/TD]
[TD]Jim[/TD]
[TD]Bob[/TD]
[TD][/TD]
[/TR]
[TR]
[TD]User2[/TD]
[TD]Bob[/TD]
[TD]Jimmy[/TD]
[TD][/TD]
[/TR]
</tbody>[/TABLE]

And the other is very similar bar a few extra columns.

I need to be able to pull the ticket number from the other worksheet for the said users.
How can i lookup the username but pull back the ticket number for that user?

If it makes it easier the columns in the sheet i need the data are:
Username (A1) Ticket Number (The missing information) (H1) i can then extend this down.

And the other sheet where i pull the information is:
Username (W) Ticket Number (this has the info i need) (AC)

Can anyone explain how to do this?