Can I request dispute or validate closed accounts?

I'm 32 and would like to buy a house for my son and I next year, so I'm trying to repair my credit. I haven't used or opened credit for anything in the last 4 years. I have several listings on my CR with the status of being closed including 2 with Asset Acceptance a collections company.

I haven't made payments on any credit within the last 3 years or even spoken to any of the original creditors or the collections agencies. They call all the time I'm just not an answer the phone kind of person, but the calls says someone has bought the accounts? Can I dispute or request to validate an account with a status of closed? Some of the listings are with original creditors and some are listed with a collections company who bought the account, but all but 2 are listed as closed with negative. My credit score is at 540 so I would like to begin having the negative removed through validate/dispute. There are no judgements against me so unless someone has a signed contract from me they are out of SOL in my state. This is true even of credit cards I opened online correct?

One kind of related question I have. There is a listing for THD/CBSD listed as a Revolving Charge Account with an open date of 3/2003 says my high balance is $2002 current balance is $0 the account status is open and they have me listed ok all the way up to Nov 2010??? In the comments it says : Account in dispute-reported by subscriber... I'm not sure if I've ever had a card with the company, I haven't disputed anything yet so I'm assuming subscriber is the creditor. Anyone know what this could be? identity theft from 2003 seems unlikly? collections agency? reporting error? any ideas on how to find out other than validate letter for a positive account? who would dispute my CR other than me and for what reasons?

The other positive account is HSBC/NEIMN which is a Neiman Marcus card opened in 2005. I only put $292 on it which is the high balance but its current balance is $0 even though I didn't pay it. It's listed as open and still reported as OK thru Nov 2010. Since almost all of my accounts are negative I don't want to dispute the two that are positive but I do want to find out what they are and why they are still open. Are writing them letters the best way to do this? I know its not the top priority in repairing my credit but just curious.

I'll post my other questions, regarding the best way to begin the process and a default student loan of 3k, in a seperate post so anyone seeking the same info can easily locate it. Sorry the post is so long I just wanted to be sure I gave enough details to get the most correct and up to date advice.

Thanks to anyone who can help me get started this is a great forum with lots of very knowledgable crontributors!