Check with your insurance company for details. Warranties vary by make and model. They do not cover software problems, and do not cover consumables such as printer cartridges. Additionally, warranties do not cover damage due to dropping, spills or other accidents. Apple warranties are one year long, while most Dell systems have three year warranties.
Upgrades are available from both vendors.
Services for other computers vary by manufacturer. Many manufacturers build all machines to order. You should allow two to four weeks for orders to be filled. Special installation disks will be available for Apple models that will simplify their configuration. Local arrangements can be made to purchase an ethernet card and have it installed if necessary.