MOSS: Working with SPFieldUrlValue
See the code below, how easy it is to set the URL field value :)
SPListItem myListItem = 'write the code to get the list item having a Link item attribute'
SPFieldUrlValue myLink = new SPFieldUrlValue();
myLink.Description = "Adeel's Blog"
myLink.Url = "http://www.weblogs.com.pk/abk"
myListItem["Name of the Link Attribute"] = myLink;
myListItem.Update();