The 1998 base XE model does not have power locks

GXE, SE and GLE models all come with standard power locks and keyless entry + security alarm

if there is a security light blinking on your dash, then you definitely have the keyless option

buy remote key from ebay for about $20, programming is easy and you can do it yourself. Also your Nissan dealer can sell you the same thing but around $70

good luck