I'm a part time developer with only limited server experience. My client is having a very bad experience with a host (IISSystems). They keep switching him to higher level plans without his authorization and then requesting more money. I am going to recommend that he switch to a new host.

The current host is really hard to communicate with and I don't think he knows what he's doing. He told me that they were running Solaris for a web server (Did you mean Apache?) and then I checked on netcraft and they are using NT and IIS.

So, I'm getting worried that the current host will not make it easy to switch, either because the guy there is hard to communicate with or just not competent.

I understand that a new host can make the DNS change request, but does the old host have to do something too? I need to understand exactly what has to happen so I can support my client if there are problems.

You just need to find a new host and then update the DNS information for the domain.
The old host needs to do nothing (unless they own the domain).

I had a similar problem, with one of the domains I (used to) own, it was stuck with a certain hosting company (I think they've gone bust since :D )

They wouldn't release the domain I purchased (they ordered it on my behalf)

I told ukname, the company i was trying to move to about this, they ended up phoning my old host (they found out the owners home phone number), who got my nameservers changed to point to ukname.net servers within 1-2 days roughly, anyway I was very impressed with ukname's commitment to it's customers.

try emailing ukname.net sales team, i'm sure they'll sort it out for you if you decide to host with them

I have heard of Hosts putting a lein on domain names for customers who have outstanding balances. I am not sure how this keeps your registar from xfering the domain but i think this can be done.

As long as you are the legal registrant of the domain name in question, they will not be able to block you from switching to a different host.

If you don't know where your domain is registered, you can find out by doing a search on www.internic.net/whois.html