I don't think you know the risks. Your question seem to imply something like "yeah, I know I can get a virus or a trojan or something, so I use an old laptop, I don't care if it gets infected"
OK, In that sense (viruses and malware), hidden services sites ( .onion sites) have THE SAME RISK as regular sites;
they both uses the same technology, like html, css, javascript, etc.
Sure, a page may try to install you something, but a regular web site has the same probability of doing that.
The risk about hidden service sites, is when people browse those sites, they want to stay anonymous.
and some bad hidden service sites may try to trick your browser so they can IDENTIFY YOU.
if you browse those sites WITH flash activated, is quite easy to find out your ip.
if the site you are visiting has illegal content, they may use flash or javascript to try to identify you and can you suffer consequences
That's the risk of TOR hidden service sites. And your ip is the same, no matter if you are using an old laptop.
chances are, if you use an old laptop, is that you are also using an old browser, that may have unfixed vulnerabilities that can be used to track you. In that case, using an old laptop is more risky.
But if you are not worried about being identified, then just relax. Onion sites are just as risky as regular sites from the point of view of viruses and stuff-that-may-damage-your-computer.
ok, one more time, THE RISK OF ONION SITES IS *NOT* GETTING YOUR PC DAMAGED, IS LOOSING YOUR ANONYMITY WITHOUT YOU EVEN REALIZING IT.
and yes, you are calling it wrong.
calling it "Deep web" is a common misunderstanding.
Deep web is parts of the regular web that cannot be indexed, for reasons like being completely dynamic, like ajax sites, flash sites.
here is what really means deep web: http://en.wikipedia.org/wiki/Deep_web
ANSWER:
Use the Tails cd.
Tails is a live cd, that has tor installed, and is configured to have flash and other thing that may expose you DISABLED.
and since is a live cd, yes, it wont get infected or anything ;) so you can click any pretty link XD (if your fear was malware)
get it here:
https://tails.boum.org/
use tails from your regular pc or your laptop (if your laptop support it) It would be as safe on any of them.
(on a side note, just to not let it pass, the other risk about tor, is when using it to visit regular sites. The end point of tor may spy your traffic if you are not using HTTPS; if you visit sites that require you to type passwords, just make sure is https - note the final S - )