Setting up Dell XPS 410 as a server

I have a home network which consists of 1-Dell XPS D300 running windows 98se, 1-Dell XPS gen 2 running windows xp pro, 1-Dell XPS gen 3 running windows xp home,1-Dell laptop Inspiron 9300 running windows xp pro,1-Gateway CX210X tablet/laptop running windows xp pro. I also have 1-Dell XPS 410 running windows xp pro.

 

I have all the pcs and laptops connected to my Linksys SRX400 wireless gateway 4 port router with a Linksys 5 port switch.

 

I have my Verizon online DSL thru this router being shared by all the pcs/laptops.

 

What I want to do is make the new Dell XPS 410 a server to the other pcs/laptops and be able to have remote access from the road so when I am away from my office I will be able to work on my business at home as well as have my Maxtor external usb harddrive hooked to the XPS 410 as a backup.

 

Any help anyone could provide would be greatly appriciated I am very technical 28 years in the alarm field. I have built and repaired pcs/laptops and have done networks, but have never done servers I am totally unsure how to do setting up of the server. I have google searched for info but no luck still cannot connect to the server.