Vostro 420 Desktop Build Quality vs Optiplex

Hi, I'm new here but I've read some of the messages previously posted. I know there was a thread about vostro verses optiplex, but I think it was about a year old. Also, when optiplex was mentioned for good build quality, it was mentioned regarding the mini-tower.

I'm currently in the market for a new computer to replace my six year old dell dimension 8250, and I'm between the vostro and the optiplex. I was assuming that the vostro desktops have poor build quality due to what I've read online, but I also heard that Dell had redesigned their vostro line. I'm wondering if poor build quality would still apply to the vostro 420 desktop? I'm not one to expand on a desktop once I purchase it, I usually leave it as it is hardware wise until I purchase a new one (some six years later.) So, I'm not concerned about it being annoying to open. But, I do want something that will last a while, and I'm assuming that build quality would reflect this.

I currently do graphic design, and use my computer basically for tasks involving that. I use multiple adobe programs at once, so I'm getting a quad core processor, and 4 GB of ram. I don't do 3d stuff or renders, so I'm not too worried about a super high end video card. I want xp, which is why I'm looking at the business models in the first place.

I'm leery of the vostro line, because I can get the 420 desktop with some high specs (Q9650, 500 GB HD, 4 GB RAM, 3 yr limited warranty) and a 22 inch ultrasharp monitor all for around 1,500 (1,200 after some instant savings). Yet, I can get an optiplex 960 with a Q9550, 4 GB RAM, a 350 GB HD, and no monitor for slightly more money. So, the specs are slightly lower and I get no monitor if I choose the optiplex option (for my price range). It just seems like if there's a 300 or so price difference between Vostro and Optiplex, Vostro must still be poorly made. Am I right in assuming this?

Anyway, if anyone can give me some advice on the quality of the 420 Vostro desktop, I'd really appreciate it. Thanks!
Michelle