Open it up and take a look inside, there is no need to match your old hard drive, a newer one will be significantly faster, if its a wide flat cable, then you need a PATA drive
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2010150014+1035907789&QksAutoSuggestion=&ShowDeactivatedMark=False&Configurator=&Subcategory=14&description=&Ntk=&CFG=&SpeTabStoreType=&srchInDesc=
If its skinny and red you need a SATA drive