If you have an existing Windows install and your repair disc, you can rebuild your MBR (info
here), but that might be a bit too tricky.
Otherwise, you should first try and recover your data, which should be only a small task with your Ubuntu Live CD that you have.
Boot the Live CD up.
Mount your windows Hard Drive (See
here for more info)
Copy the data you wish to recover to an external hard drive
Verify the data has been transfered (and is readable with another PC if possible)
Then you can just boot to your Dell recovery Disc and follow the prompts to reinstall